In 1958 post-war Britain, Stevens, the butler of Darlington Hall, receives a letter from Miss Kenton, a former colleague employed as the housekeeper some twenty years earlier, now separated from her husband. Their former employer, The Earl of Darlington, has died a broken man, his reputation destroyed after he was exposed as a Nazi sympathizer, and his stately country manor has been sold to a retired United States Congressman, Mr. Jack Lewis. Stevens is granted permission to borrow Lewis’ Daimler, and he sets off to the West Country to see Miss Kenton, in the hope that she will return as housekeeper.
The film flashes back to Kenton’s arrival as housekeeper in the 1930s. The ever-efficient Stevens manages the household well, taking great pride in and deriving his entire identity from his profession. Miss Kenton, too, proves to be a valuable servant, and she is equally efficient and strong-willed, but also warmer and less repressed. Stevens and Kenton occasionally butt heads, particularly when she observes that Stevens’ father (also a former butler) is in failing health and no longer able to perform his duties, which Stevens stubbornly refuses to acknowledge. Stevens’ professional dedication is fully displayed when, while his father lies dying, he steadfastly continues his butler duties.
Relations between Stevens and Kenton eventually thaw, and it becomes clear she has feelings for him. Despite their proximity and shared purpose, Stevens’ outward detachment remains unchanged; his first and only loyalty is to his service as Lord Darlington’s butler. In a scene of agonized repression, Miss Kenton embarrasses Stevens when she catches him reading a book. Curious, she forces it out of his hand, and finds to her disappointment it is an ordinary romance novel; Stevens explains to Miss Kenton he was reading it only to improve his vocabulary, and asks her not to invade his private time again.
Meanwhile, Darlington Hall is regularly frequented by politicians of the interwar period, and many of Lord Darlington’s guests are like-minded, fascist-sympathizing British and European aristocrats, with the exception of the more pragmatic Congressman Lewis, who does not share the “noble instincts” of Lord Darlington and his guests. Lewis informs the “gentleman politicians” in his midst that they are meddling amateurs and that “Europe has become the arena of Realpolitik” and warns them they are “headed for disaster.” Later, Lord Darlington’s aristocratic guests grill Stevens about his political knowledge to prove that the lower classes are ignorant and unworthy to have an opinion, but Stevens steadfastly refuses to acknowledge that he has ever listened to their conversations, being too busy serving.
Darlington later meets Prime Minister Chamberlain and the German Ambassador, and uses his influence to try to broker a policy of appeasement towards Nazi Germany, based on his belief that Germany had been unfairly treated by the Treaty of Versailles following the First World War and only desires peace. In the midst of these events, and after overhearing Sir Geoffrey Wren praising Nazi racial laws, Darlington suddenly requests that two newly-appointed German-Jewish maids, both refugees, should be dismissed, despite Stevens’s mild protest that they are good workers. Nevertheless, Stevens carries out Lord Darlington’s command, despite a horrified Miss Kenton threatening to resign in protest. Miss Kenton later confides in Stevens that she has no family and nowhere to go should she leave Darlington Hall, and is ashamed to not follow up on her threat to resign. Stevens does not mention that he disagreed with Lord Darlington’s order and leaves Miss Kenton with the impression that he didn’t care about the girls’ fate.
Lord Darlington’s godson, journalist Reginald Cardinal, is appalled by the nature of the secret meetings in Darlington Hall. Concurring with Congressman Lewis’ earlier protestations, Cardinal tells Stevens that Lord Darlington is a pawn, being used by the Nazis. Despite Cardinal’s indignation, Stevens does not denounce or criticise his master, feeling it is not his place to judge his employer’s honorable intentions, even if they are incorrect. Later, Lord Darlington expresses regret for having dismissed Ilsa and Irma, the two German-Jewish maids. He asks Stevens to locate them and Stevens questions Miss Kenton as to the maids’ whereabouts. (It is revealed they had returned to Germany, but their ultimate fate is unknown.)
Eventually, Miss Kenton forms a relationship with a former co-worker, Tom Benn, who proposes marriage and asks Miss Kenton to move away with him to run a coastal boarding house. Miss Kenton mentions this proposal to Stevens, in effect offering him an ultimatum, but Stevens will not admit his feelings, offering Miss Kenton only his congratulations. Miss Kenton leaves Darlington Hall prior to the outbreak of the Second World War. Before Miss Kenton’s departure, Stevens finds her crying in frustration, but the only response he can muster is to call her attention to a neglected domestic task.
En route to meeting Miss Kenton in 1958, when asked by locals about his former employer, Stevens at first denies having served or even having met Lord Darlington, but later admits to having served and respected him. He says that, while Lord Darlington was unable to correct his terrible error, he is now on his way in the hope that he can correct his own. He meets Miss Kenton (though separated, still Mrs. Benn), and they reminisce. Stevens mentions in conversation that Lord Darlington’s godson, Reginald Cardinal, was killed in the war. He also says Lord Darlington died from a broken heart after the war, having sued a newspaper for libel, losing the suit and his reputation in the process. Stevens reveals that in his declining years, Lord Darlington at times failed to recognise Stevens and carried on conversations with no one else in the room.
Miss Kenton declines Stevens’s offer to return to Darlington Hall, wishing instead to remain near her grown daughter, whom she has just that day learned is pregnant. She also implies that she will go back to her husband, because, despite being unhappy in their marriage for many years, in all the world he needs her the most. As they part, Miss Kenton is emotional, while Stevens is still unable to demonstrate any feeling. Back in Darlington Hall, Lewis asks Stevens if he remembers much of the old days, to which Stevens replies that he was too busy serving. A pigeon then becomes trapped in the hall, and is eventually freed by the two men, leaving both Stevens and Darlington Hall far behind.