The film begins with an elderly World War II veteran (Harrison Young) and his family visiting the Normandy American Cemetery and Memorial at Colleville-sur-mer; Normandy, France. The veteran collapses to his knees in front of a gravestone, overwhelmed by emotion. The scene then changes to the beginning of the Normandy invasion, with American soldiers landing on Omaha Beach and struggling against dug-in German infantry, machine gun nests and artillery fire. One of the officers who survives the initial landing, Captain John H. Miller (Tom Hanks), commanding officer of C Company, 2nd Ranger Battalion, assembles a group of soldiers and slowly penetrates the German defenses, leading to a breakout from the beach.
Meanwhile, in the United States, General George C. Marshall discovers that three of the four brothers of the Ryan family have all died within days of each other and that their mother will receive all three notices on the same day. He learns that the fourth son, Private First Class James Francis Ryan (Matt Damon) of Baker Company, 506th Parachute Infantry Regiment is missing in action somewhere in Normandy. After reading to his staff Abraham Lincoln's Letter to Mrs. Bixby, Marshall orders that Ryan be found and sent home immediately.
Back in France, Miller receives orders from his battalion commander, Lieutenant Colonel Walter Anderson (Dennis Farina), to find Ryan. He assembles six Rangers from his company (Tom Sizemore, Edward Burns, Barry Pepper, Vin Diesel, Giovanni Ribisi, and Adam Goldberg), plus one man detailed from the 29th Infantry Division (Jeremy Davies), who speaks fluent French and German, to accomplish this task. With no information about Ryan's whereabouts, Miller and his men move out to Neuville. On the outskirts of Neuville they meet a platoon from the 101st. After entering the town Private Adrian Caparzo (Diesel) is fatally wounded by a sniper and dies. They locate a Private James Fredrick Ryan from Minnesota (Nathan Fillion) but soon realize their mistake. They find a member of Charlie Company, 506th, who informs them that his drop zone was at Vierville. He also tells them that both Baker and Charlie companies have the same rally point. Once they reach the rally point, Miller locates a friend of Ryan's, who reveals that Ryan is defending a strategically-important bridge over the Merderet River in the fictional town of Ramelle.
On the way to Ramelle, Miller decides to take the opportunity to neutralize a small German machine gun position close to an abandoned radar station. Technician Fourth Grade Irwin Wade (Ribisi), their medic, is fatally wounded in the ensuing skirmish. The last surviving German, known only as "Steamboat Willie" (Joerg Stadler), incurs the wrath of all the squad members except Technician Fifth Grade Timothy E. Upham (Davies), who protests to Miller about letting the squad kill the German soldier. Miller decides to let the German walk away and surrender himself to the next Allied patrol, a decision viewed by Private First Class Richard Reiben (Burns) as letting the enemy go free. No longer confident in Miller's leadership, Reiben declares his intention to desert, prompting a tense confrontation with Technical Sergeant Michael "Mike" Horvath (Sizemore) that threatens to tear the squad apart, until Miller defuses the situation by revealing his origins, on which the squad had formed a betting pool; Miller is an English teacher and high school baseball coach in the fictional town of Adley, Pennsylvania. Reiben remains with the group.
The squad finally arrives on the outskirts of Ramelle where they destroy a German mechanized reconnaissance unit with the help of some American paratroopers, one of them being Ryan. The unit regroups in Ramelle, joining with the American paratroopers defending the town, where Miller informs Ryan of his brothers' deaths and of their mission to bring him home. Ryan adamantly refuses to leave his makeshift unit, demanding that he remain to help defend the bridge against an impending German counterattack. Miller reluctantly agrees and orders his unit to help defend the bridge in the upcoming battle, taking command and setting up the defense with what little manpower and resources they have. There are fewer than twenty American soldiers in the town.
The Germans arrive in force supported by two Tiger I tanks, two self propelled guns, a towed FlaK 38 cannon, and half-tracks. Miller leads the defense, but in spite of inflicting heavy German casualties, most of his remaining squad members are killed. While attempting to blow the bridge, Miller is shot by "Steamboat Willie",who has reunited with the German Unit in town, and is fatally wounded. Just before a Tiger reaches the bridge, an American P-51 Mustang arrives and destroys the tank, followed by more Mustangs and advancing American infantry and M4 Sherman tanks who assault the town and rout the remaining German forces. Upham executes "Steamboat Willie", having witnessed him shooting Miller. Ryan, Reiben and Upham are the only main characters to survive the battle, and Ryan is with Miller as he dies and hears his last words, "James... earn this. Earn it."
Back in the present, the elderly veteran is revealed to be Ryan at Miller's grave. Ryan asks his wife to confirm that he has led a good life and that he is a "good man", and thus worthy of Miller's and the others' sacrifice. He then salutes Miller's grave as the camera pans down the gravestones to the American flag.