In the opening scene, US Navy SEAL sniper Chris Kyle (Bradley Cooper) is perched on a rooftop, scoping out the path of a US military convoy through his sniper rifle. He sees a man on a rooftop talking on a cell phone, and he appears to be watching the convoy, which Kyle reports it through his headset. He is told that if the man is reporting troop movement, he has the green light to shoot him, but Kyle is unsure. His marine backup suggests that he may just be talking to his girlfriend on the phone. The man disappears from the rooftop and a few moments later, a woman and a young boy appear in the doorway of the same building and walk toward the convoy. Kyle reports the woman and boy, noting that the woman is not swinging her arms as she walks and appears to be carrying something. No one in the convoy can see it to confirm. He watches through the scope as the woman removes something from her cloak and hands it to the boy, and he realizes that it is a grenade. He again gets the green light to shoot, but his marine guard warns him that he will be sent to prison for shooting a child, if he's wrong.
The film cuts to a young Chris hunting with his father, and he shoots and kills a deer. His father congratulates him on his excellent shot, telling him he has a gift. Chris happily approaches the deer, dropping his gun to the ground as he runs to it. His father reprimands him for treating his gun cavalierly.
Over several scenes set in his childhood, we see young Chris, his younger brother Jeff and his parents attend church, where he pockets a small well-worn copy of the New Testament. There's also a scene of Jeff being beat up by a much larger kid on a playground. Chris runs up and pulls the bully off, beating him up. In the next scene, seated at the family's dinner table, Chris' father tells the boys that there are three kinds of people in the world - sheep, wolves and sheepdogs. Sheep don't believe that there is evil in the world, wolves are predators who commit evil, and sheepdogs are blessed with the aggression and bravery to protect the world from evil. The speech clearly makes an impact on Chris.
Years later, Chris is competing in rodeos with his younger brother traveling alongside him. He returns home one night and finds his girlfriend in bed with another man. He hits the man several times and kicks him out before turning around to kick his girlfriend out. She complains that he abandons her every weekend to go to rodeos, believing himself to be a cowboy when he's just a failed farmer.
As Chris and his brother watch TV, they see the news of the August 1998 terrorist attacks on the US embassies in Tanzania and Kenya. Chris is angry that US citizens are being attacked and feels compelled to do something to protect his country.
He visits a US navy office and talks to the recruiter. The recruiter suggests that Kyle might be interested in the SEAL program and hands him a pamphlet, but Kyle remarks that he's not much of a swimmer. The recruiter takes the pamphlet out of his hand and says that it's not for most men, but Kyle retorts that he's not most men.
Kyle goes through the rigorous training process, which includes being blasted with a powerful hose while exercising, laying down on the beach and letting the cold surf wash over him as well as being verbally harassed by the officers who run training, mocking him for being too old to be a SEAL at the age of 30. He also goes through sniper training, bringing in his hunting background. The instructor reminds them to 'aim small, miss small' - if they aim for a button on a man's shirt, they might miss by only two inches, but if they aim for the shirt altogether, they might miss by two feet. His instructor also tells him to keep his non-scoping eye closed, to better focus on the target. Kyle responds that he needs to keep both eyes open to see what else is out there. The instructor tells him that they are shooting at a target, and there's nothing else out there, and reprimands him with 50 push ups. Kyle proves him wrong by shooting a snake, hidden in the grass on the shooting range.
In the mean time, Kyle meets a woman named Taya (Sienna Miller) at a bar one night. She tells him that she would never marry a SEAL, as her sister did but was cheated on and lied to constantly. She also challenges him at drinking shots, showing off how tough she is, but she ends up vomiting outside the bar. Kyle is kind to her, holding her hair back and taking care of her. He calls her repeatedly until she agrees to date him, and their relationship progresses. She asks him at one point if she ever thinks about who will be at the end of his gun, and he tells her that he just wants to protect his country. On their wedding day, he and his fellow SEALs receive word that they will be deployed to Iraq, which they celebrate.
The film cuts back to the opening scene and Kyle watches the woman hand the grenade off to the young boy. As the young boy starts running toward the convoy with the grenade in his hand, Kyle pulls the trigger and kills him. The woman starts wailing and running toward the boy, and Kyle watches her closely. The woman runs past the boy's body to grab the grenade he dropped and continue running at the convoy. She is about to fling the grenade at it when Kyle shoots her. The grenade falls short of the convoy and explodes, leaving the troops unharmed.
Kyle returns to the base camp where a fellow SEAL congratulates him on his first kill. Kyle doesn't appear to regret the killing but admits that he didn't think this is what it would be like to protect his country.
Kyle continues to provide overwatch for marine units who are going door-to-door through an evacuated city, searching for an al Qaeda leader named Zarqawi. They are told that any military-aged male who remained in the city should be considered a threat. Kyle successfully watches over the troops, shooting many would-be attackers who carry guns and bombs. Kyle is dedicated to his job, even urinating in his post to avoid abandoning his watch. After a particular watch, Kyle reports that he had six kills, which is more than all the other snipers combined in the same shift. His fellow troops begin calling him The Legend. Also, a bounty has been placed on their heads by al Qaeda. Kyle also hears of an al Qaeda sniper who won a gold medal for shooting in the Olympics called Mustafa, known for making nearly-impossible shots.
Several times throughout, Kyle talks to his pregnant wife on the phone and she tries to get him to be honest and tell her about what he's going through. He resists but they talk and laugh together. She complains that she has to put the crib together by herself and they express how much they miss each other. She also tells Kyle that his younger brother has been deployed to Iraq as well.
At times, Kyle complain about being assigned to overwatch as he wants to be on the ground with the troops going door-to-door. He believes his training makes him better equipped than the Marines doing the job, and he can't protect them on overwatch once they're inside a building. He finally abandons his overwatch post and joins the Marines on the ground who welcome The Legend. As they go door to door they find a home where the family has refused to evacuate. The man tells them that it is his home, and he will not abandon it. Kyle questions the man with the help of an interpreter, showing him a picture of Zarqawi and asks him if he knows who he is. The man says that Zarqawi's second in command is a man known as the Butcher. He can give Kyle information on the Butcher, but he wants $100,000 in return. Kyle promises to help him, and the man provides a name. Kyle has the name checked out, which turns out to be useful intelligence, so they prepare to bring the cash to the man.
As the SEALs drive back to the man's home to bring him the money, Kyle calls Taya, who tells him that she has just learned their baby is a boy. Kyle is overjoyed when his vehicle is suddenly attacked and he drops the phone while it is still connected. Taya listens in horror to gunfire and screaming, unsure of what is going on. Mustafa is shooting at the men, and Kyle tries to take him out but is unable to do so as he is pinned down by gunfire. The Butcher found out that the man gave up information to the troops, and he kills the man's young son with a handheld power drill. He also shoots the man and screams out a warning to anyone who cooperates with the US military. The Butcher and Mustafa both get away unharmed. More troops arrive, and Kyle and his men are able to get out safely. A few days later, the troops return and Taya tearfully reunites with Kyle.
Kyle tries to adjust to life back at home. Taya finds Kyle watching a video of US soldiers being killed by a sniper and rushes to shut it off when he sees her. She tells him that she wants him to open up, but he doesn't want her to know about the atrocities they're facing in Iraq. The video shows Mustafa's kills, which he records and sells.
While at the obstetrician's office for a check up, the doctor asks him how he's doing, to which he responds that he's fine. She takes his blood pressure which is very high at 170/110. Both the doctor and Taya are extremely concerned about him, but Kyle brushes off their concerns and says he will take care of it. As they drive away, Taya tries to get him to open up, but Kyle just repeats that he's fine. However, as he's talking, he grows more frustrated as he tells her that he doesn't understand why everybody isn't talking about what's going on in Iraq and how people are just going about their every day lives. Taya goes into labor and they rush to the hospital where she gives birth to their son.
After arriving in Iraq, Kyle sees his younger brother marching with his troop. Kyle cheerfully greets Jeff who is about to be sent home and is much more battle-worn and conflicted. Jeff wearily walks away and tells Kyle, "fuck this country."
Kyle redeploys for a second and third tour in Iraq, continuing to hunt down the Butcher. The bounty on his head has been increased, and he jokes that his wife may go after it herself. In their search for the Butcher, Kyle leads a team of SEALs, including men he has served with for a long time, and they are clearly a close-knit group. One of his men, Mark begins to express regret about the war, and Kyle reminds him that they are patriots serving their country and protecting their families.
On one mission, the team gets intelligence that the Butcher may be hiding out in a particular building. The team breaks into a home across the street from the building though the man that lives there with his family says that they have no knowledge of any terrorist activity. The SEALs watch the building from the home, realizing they will have a hard time getting in when the man tells them that it is a holiday and he wants to invite them to be guests at his table. The SEALs join them for a meal, eating and talking boisterously. The man reaches across the table to his son, and Kyle notices that his elbows are rubbed raw. Since snipers often spend considerable amounts of time held up on their elbows, causing callouses like the ones the man has, this tips him off that the man might not be as innocent as he professed. He gets up under the pretense that he's going to the bathroom and searches the apartment until he finds a hidden compartment in the floor filled with guns and weapons. He returns to the dining table, taking the man into the other room and showing him what he has found. He tells the man that he will help the SEALs get into the building. At gunpoint, they force the man to knock on the door. The door opens to allow the man in, as he is clearly known to the people inside, when a sniper takes out the door opener. The man grabs the door opener's gun and tries to shoot at the SEALs who take him out. The SEALs enter the building, clearing room after room looking for the Butcher who escapes through back tunnels.
While at an auto body shop, a young Marine approaches Kyle and tells him that Kyle had saved his life once in years past. The Marine asks Kyle if he would go down to the VA sometime to talk with veterans. He also talks with Kyle's son, telling him that his father is a hero and allowed him to go home to his own daughter. Kyle is gracious but feels uncomfortable with all the praise the young man gives him.
Between deployments, Kyle continues to struggle to readjust to civilian life. Loud noises seem to startle him deeply. Taya gives birth to their second child, a daughter. When Kyle visits the hospital, he sees his daughter in the nursery and she begins to cry. The nurse is handling another baby and doesn't immediately attend to Kyle's daughter, and he becomes increasingly agitated, screaming at the nurse. His wife bitterly remarks that he is missing his kids' childhoods, and she has to create memories by herself. He argues that he is protecting the family and his country by doing his job, but Taya wants him to protect them at home.
In a casual conversation, another SEAL, Biggles reveals that he's purchased an engagement ring locally to save money. The men tease him about the quality and possible blood origins but Biggles laughs it off and says he will tell his girlfriend it's from Zales. In an ensuing battle, Biggles is shot in the face by Mustafa and they rush him back to the base where he goes into surgery. Biggles asks Kyle to promise to deliver the engagement ring he bought to his girlfriend back home, no matter what happens. The troops head back out immediately, burning to get revenge and Mark is shot during the mission and presumably killed. Biggles survives and is brought stateside for medical treatment.
After his third tour, Kyle still cannot connect with his family and his home life. He visits Biggles in the hospital who seems to be in good spirits. Biggles shares that he is now engaged, having purchased a new ring that is actually from Zales, despite trying to warn his girlfriend that her life will be much more difficult being married to him. Kyle doesn't seem to comprehend what could be difficult about being marring to a SEAL, saying she's lucky to be married to a patriot who fights for his country.
Kyle still feels compelled to return to the war. He fights with his wife about it, with Taya demanding to know if he has a death wish. She says he's done his duty and it's somebody else's turn to go. She also tells him that if he leaves again, she and the children will not be waiting for him when he returns. He tries to smooth things over but deploys yet again.
Kyle tries to call Taya but it goes to voice-mail. While talking with another SEAL, Kyle finds out that Biggles has died in a recent surgery stateside. During one overwatch post, Kyle watches a man walks out onto the street carrying a grenade launcher. Kyle kills the man. A young boy who had been playing nearby is startled and runs over. Kyle is concerned that the young boy will try to pick up the grenade launcher and he will have to kill him. The young boy struggles to get the grenade launcher on his shoulder, and Kyle prepares himself to shoot the boy. The boy finally gives up and runs away, and Kyle is clearly relieved.
Kyle and his team are told that engineers are trying to construct a wall around the city but a sniper keeps picking them off from over 1,000 yards away, leading the team to believe it is Mustafa.The team is sent out despite an oncoming sandstorm to try to take him out and protect the troops constructing the wall. They head out into the city and take their places on a rooftop, aiming at the direction they believe Mustafa is shooting from. However, Mustafa moves quickly and shoots from a different angle, killing another soldier constructing the wall, causing the SEALs to scramble to change their set up.
Kyle believes he's spotted Mustafa through the scope though the rest of the team has a hard time believing him, as he's over 2,000 yards away. They don't think he can see Mustafa let alone shoot him at that distance. Also, the team spots many insurgents walking around the building and if Kyle takes a shot, it will alert them to the SEALs' location where they will be vastly outnumbered. The leader calls in a response team from the base, which will take some time to arrive. They warn Kyle not to take the shot and endanger them all until they have backup. One of the SEALs encourages Kyle to take the shot if he believes he can do it.
Kyle takes the shot, killing Mustafa, but the insurgents hear the gunshot and swarm the roof. The four SEALs try to conserve their ammo and take out the terrorists one by one that are rushing in on them. The backup is on its way but hasn't yet arrived so the men are on their own. Kyle tearfully calls Taya and tells her that he's ready to come home. The men shoot their way off the roof as the backup finally arrives as does the sandstorm. The men try to run into the vehicle but they have little to no visibility, struggling to see the truck, shoot the insurgents and protect each other. Three of the SEALs run into the truck bed but Kyle falls behind when he's shot. They slow down for him and he barely makes it back into the truck.
Kyle returns home. He is still not connected to his home life. At a family barbecue, Taya catches him watching the TV intently as if it were on, when it is actually off. She tries to get him to join the party, and they watch the children play. A dog grabs the collar of a boy and is tugging at it. Kyle suddenly rips off his belt and grabs the dog as if he might beat or strangle it until Taya cries out in horror.
Kyle goes to a doctor who tells him that according to his military records, Kyle has been credited with 160 kills, more than anyone else in US history. The doctor asks if he has any regrets about killing those people, and Kyle's response is that he doesn't regret that, he only regrets not saving more American troops. The doctor tells him that there are American troops who could use his help at home. He takes Kyle to a support group of disabled veterans, many of whom have lost limbs. The men share their stories, and Kyle decides to take some of the men out to a shooting range and teach them to shoot sniper rifles. After hitting a target, one of the men remarks that it's the first time he's felt like a man since he was injured in battle.
Kyle has finally regained himself, playing with his children and connecting with his wife. He teaches his young son to hunt, telling him that it's serious business to end a heartbeat. He continues his work with veterans. Taya tells him how proud she is of him, for finding himself and finding his way back to his family. He tells her that a Marine's mom reached out to him, asking if he would help her son out who's been struggling since his return. Kyle opens the door and an uneasy young man waits for him by his truck while Taya watches. The door closes, and the final credits reveal that the troubled young Marine killed Chris Kyle i.e. 'Chris Kyle was killed that day by a veteran he was trying to help'.