On June 6, 1944, the U.S. Army lands at Omaha Beach as part of the Normandy invasion, incurring major losses against the artillery and machine gun fire of the heavily fortified German forces. Initially dazed by the chaotic battle, 2nd Ranger Battalion Captain John H. Miller takes command of a surviving group and leads a successful infiltration behind German lines to secure victory.
The United States Department of War receives communication that three of four Ryan brothers have been killed in action; the last, James Francis Ryan of the 101st Airborne Division, is listed as missing. General of the Army George C. Marshall orders that Ryan be found and sent home, to spare his family the loss of all its sons. Miller is tasked with recovering Ryan and assembles a detachment of soldiers to accompany him: Mike Horvath, Richard Reiben, Adrian Caparzo, Stanley Mellish, Daniel Jackson, Irwin Wade, and interpreter Timothy Upham, who lacks any combat experience.
The group tracks Ryan to the town of Neuville-au-Plain, where Caparzo is killed by a German sniper while trying to rescue a young girl. Mourning their friend, the men grow resentful at being forced to risk their lives for one man. They later find James Frederick Ryan, but realize he is the wrong man with a similar name. That evening, the men rest in a chapel, where Miller tells Horvath that his hands began uncontrollably shaking after he joined the war. The men travel to a rallying point where the 101st Airborne might be after landing off course, where they find masses of wounded and displaced soldiers. Wade admonishes Reiben, Mellish, and Jackson for callously searching through a pile of deceased soldiers' dog tags in front of passing troops, hoping to find Ryan's among them and conclude their mission. Remorseful for ignoring their behavior, Miller shouts for anyone that knows Ryan; one deafened soldier tells him that Ryan was reassigned to defend a vital bridge in the town of Ramelle.
On the way, Miller decides to neutralize a German gun nest they discover, against the advice of his men, and although they are successful, Wade is killed. The men decide to execute a surrendered German soldier in revenge, but Upham intervenes, arguing that they should follow the rules of war. Miller releases the soldier, nicknamed "Steamboat Willie", ordering that he surrender to the next Allied patrol. Frustrated, Reiben threatens to desert, leading to a standoff between the men that Miller defuses by revealing his civilian background as a teacher and baseball coach, which he has always refused to disclose. Miller muses that people often guessed his career before he became a soldier, while his men could not, implying that war has changed him, and worries whether he is still the man he was or that his wife will recognize him.
In Ramelle, Miller's detachment finds Ryan and informs him of their mission, but Ryan refuses to abandon his post or his fellow soldiers, believing he does not deserve to go home more than anyone else. Horvath convinces Miller that saving Ryan might be the only truly decent thing they can accomplish during the war. Miller takes command of Ryan's group as the only officer present and prepares the soldiers for a German assault. Jackson and Horvath are killed, and Upham stands paralyzed with fear as Mellish is stabbed to death. Steamboat Willie returns and shoots Miller before reinforcements arrive to defeat the Germans. Upham confronts Willie, who attempts to surrender again, and kills him, before sending the other surrendering Germans away. Upham and Reiben observe as the mortally wounded Miller tells Ryan to earn the sacrifices made to send him home.
Decades later, an elderly Ryan and his family visit Miller's grave at the Normandy Cemetery. Ryan expresses that he remembers Miller's words every day, lived his life the best he could, and hopes he has earned their sacrifices.
