18th century rural Ireland. After his father is killed in a duel, Redmond Barry lives with his mother. Barry's cousin, Nora Brady, gives him a ribbon as a sign of her feelings. Captain John Quin arrives, recruiting for the Seven Years War.

At a dance, Nora partners Quin five times and Barry none. Barry furiously returns Nora's ribbon, whereupon Quin angrily reveals that he also has one. The Bradys try to placate him. Later, Nora's engagement to Quin is toasted but Barry throws his glass at him. Barry is escorted home and it is explained that Quin earns £1,500 a year and has promised to pay off Nora's father's debts. Undaunted, Barry demands a duel. Captain Grogan (Barry's second) offers ten guineas if he apologises and goes to Dublin, but Barry refuses. Quin is hit and Barry flees. On the journey his money and horse are stolen.

With no other option, Barry joins the army. He is taunted by a bully and the argument is settled with a boxing match, which Barry wins easily. Grogan joins the battalion and tells Barry that the Bradys faked the duel as Quin was afraid to marry Nora while Barry was around. In a battle, Grogan is shot and rescued by Barry. Grogan gives him 100 guineas and dies.

To escape the army, Barry steals a messenger's papers. On the way to Bremen, a German girl gives him a meal and Barry stays for several days. Continuing his journey, he meets Captain Potzdorf, who realises that Barry is a deserter and gives him the chance to join the Prussian army rather than be arrested. The Prussian army proves infinitely worse than the English. In a battle Barry rescues Potzdorf and is decorated.

After the war Barry joins the police, where Potzdorf orders him to watch the Chevalier de Balibari, a gambler suspected of being a spy. However, as an exile, Barry is overcome when he hears the Chevalier's Irish accent and confesses everything. They agree that Barry will give detailed but anodyne reports while helping the Chevalier cheat at cards. When the Chevalier is challenged to a duel, Potzdorf decides to have him escorted out of the country. Barry substitutes for him and thus both escape.

Barry and the Chevalier continue their careers at courts throughout Europe, Barry's swordsmanship ensuring payment. Barry meets the Countess of Lyndon, who has a crippled husband, Sir Charles, and a son, Viscount Bullington. Within six hours she has fallen in love with Barry, who does everything to foster this. Sir Charles challenges Barry to admit that he is having an affair and is so affronted by the response that he dies.

Barry marries Lady Lyndon and changes his name to Barry Lyndon. Bullingdon disapproves, especially when, after the birth of Brian, Barry continues whoring while Lady Lyndon stays at home. Barry beats Bullingdon, while Brian's every whim is indulged. Barry's mother incites him to try to get a peerage and, encouraged by Lord Wendover, Barry spends a fortune pursuing the claim. Bullingdon fights Brian and, after being beaten by Barry, says he will kill Barry if it happens again.

Bullingdon denounces Barry and the marriage at a concert and Barry violently beats him in public. Bullingdon leaves home. Barry is ostracised and, with rumours of insolvency, creditors send their invoices. Brian learns that his birthday present is a horse and steals away a few days early to ride it, but he has an accident and dies. Barry begins to drink, Lady Lyndon takes consolation in religion, while Barry's mother takes control of the house. Lady Lyndon attempts suicide.

Bullingdon returns and challenges Barry to a duel. Barry deliberately misses, but, despite fear making him vomit, Bullingdon shoots Barry. Bullingdon arranges to tell Mrs Barry what has happened so that she will leave to join Barry. In a rundown inn, Barry has his leg amputated. A servant brings Bullingdon's proposal that Barry should receive 500 guineas per year, provided he leaves England. Burdened with debt, Barry is forced to accept. It is thought that Barry went to the continent, perhaps resuming his gambling career.

A final title card reminds us that all those in the story, 'good or bad, handsome or ugly, rich or poor', are now equal.