Early in the film, the narrative moves to Adolf Hitler's 56th birthday on April 20, 1945. Traudl Junge resides in the Führerbunker. Generals Wilhelm Burgdorf and Karl Koller indicate the Soviet Army is only 12 kilometres from the city center. At his birthday reception Hitler resolves to stay in Berlin and rejects a diplomatic solution. Certain officers agree that the Führer has lost all sense of reality. Later Hitler discusses his new scorched earth policy with Albert Speer, who begs mercy for the German people, saying that Hitler's plans will return them to the Middle Ages. Hitler claims that the German people have shown themselves too weak to win the war and therefore must be exterminated. Later, Eva Braun holds a party for the bunker inhabitants, but Soviet artillery fire ends the party early.
In the bunker, Hitler discusses the situation with the generals, believing that Waffen SS General Felix Steiner will save them. However, Steiner cannot mobilize enough men. Upon learning this, Hitler dismisses all except the four highest-ranking generals. While furiously accusing the Wehrmacht of sabotaging him from day one, he realizes that the war is lost and states that he would prefer suicide over surrender. Later Hitler, Eva, Junge and Gerda discuss various means of suicide. Hitler proposes shooting oneself through the mouth, while Braun mentions taking cyanide. Hitler then gives Gerda and Junge one cyanide capsule each. Eva Braun and Magda Goebbels type goodbye letters, Braun to her sister and Goebbels to her adult son Harald Quandt.
General Wilhelm Keitel is ordered to find Admiral Karl Dönitz, whom Hitler believes is gathering troops in the north, and help him to plan an offensive to recover the Romanian oilfields. Sgt. Rochus Misch, Hitler's radio operator, receives a telegram from Hermann Göring, head of the Luftwaffe. Martin Bormann reads the telegram to Hitler, where Göring asks permission to assume command of the Reich and asks for acknowledgment by 10 PM, at which time he will assume authority in the absence of a response. Considering this treason, Hitler orders Göring's arrest and removal from office.
General Weidling reports that the Russians have broken through everywhere. There are no reserves and air support has ceased. General Mohnke states the Red Army is now only 300 to 400 meters from the Reich Chancellery and that they can hold out for a day or two at most. Before leaving, Hitler reassures the officers that General Walther Wenck will save them all.
On Hitler's wedding day, Traudl takes dictation of the Führer's political testament. Hitler has ordered Joseph Goebbels to leave Berlin, but Goebbels intends to ignore the order. Hitler marries Eva Braun. When Günsche later brings a reply from Keitel that the main armies are encircled or cannot continue their assault, Hitler states that he will never surrender. He also forbids all officers to surrender or face immediate execution.
Eva Braun has her last conversation with Traudl. She gives her one of her best coats and advises her to escape. Hitler has his final meal in silence with Constanze Manziarly and his secretaries. He bids farewell to the bunker staff, gives Magda Goebbels his Golden Party Badge (marking original members of the NSDAP) and retires to his room with Eva Braun. Despite Magda Goebbels' pleas, the pair commit suicide. Rather than live in a world without Nazism, Herr and Frau Goebbels poison their children and commit suicide themselves. All the bodies are burned outside the bunker complex.
Most of the bunker survivors attempt to escape, but die at the hands of Red Army infantrymen. Junge makes her way through the Russian lines. The film ends with Junge escaping Berlin by bicycle. The fates of the film's main surviving characters are told, before the credits roll.