At the opening of the film Redmond’s father is shown being killed in a duel. We learn that Barry is in love with his cousin, Nora but she is engaged to Captain Quinn. Rather than give up on her, Redmond challenges Quinn to a duel which he wins. But he must now leave home for Dublin in order to avoid going to jail. He’s robbed on the way and joins an English Regiment. Soon after Captain Grogan arrives to tell him that the duel between he and Quinn was a ruse to get Redmond out of the picture. Nora and Quinn have married. Grogan is then killed in battle and Redmond sees the price of war for the first time. He decides he wants to abandon his service and steals a ranking officers uniform and identity papers. But a Prussian Officer catches him and forces him into the Prussian army after beating him.
Redmond endures years of service to the Officer on the battlefield and after gaining the man’s trust he is offered the opportunity to become a spy on the Chevalier du Balibari who is a fellow Irishman. Redmond accepts, but bursts into tears when in the presence of the Chevalier as he can’t contain his love of his people in Ireland and how much he misses home. The Chevalier takes Redmond under his wing and is able to get him across the frontier line into safety and away from the Prussian army. Redmond begins gaming with the Chevalier and learning how to swindle people, but soon realizes there is very little money and true opportunity for increase in it. Thus he begins his pursuit of a wealthy woman in order to increase his standing in society. He sets his eyes on Lady Lyndon whose husband is near death, and shortly after passes away.
Redmond and Lady Lyndon are married a year later and it is clear that he has done so for her wealth and status. He has no regard for her nor her son who he begins a feud with at a young age. He and Lady Lyndon have a son together and he cheats on her with multiple women. Finally he is caught and is forgiven by Lady Lyndon. His mother moves onto the estate and urges Redmond to gain a title as Lord or he will have no money nor status if Lady Lyndon dies as all will be left to her son. Redmond then begins spending extraordinary amounts of money on dinner parties, paintings and lands in order to gain the company of the Lords and Ladies of England who can back his claim to become a Lord.
His feud with his step son, Lord Bullingdon grows to a head as the young man makes a mockery of Redmond and Lady Lyndon in public. Redmond attacks him in front of the Lords and Ladies and soon loses all of their support as they disassociate themselves with him and his family. Bullingdon leaves and while gone Bryan, Redmond’s son asks for a horse for his birthday with Redmond buys for him. The boy goes to ride the horse before it is broken in and is thrown off, paralyzing him. He dies and Lady Lyndon goes into a state of grief that leads to a suicide attempt which she lives from, and Redmond becomes a drunkard.
With all of the occurring Redmond’s mother takes over the business affairs of the estate and fires Reverend Samuel who goes straight to Lord Bullingdon. Bullingdon returns to the Lyndon estate to challenge Redmond to a duel. Redmond forfeits his shot and in return Bullingdon shoots him in the leg and wins. His leg has to be amputated and Lord Bullingdon offers him 500 guineas a year for life to leave England and never return, not even for his wife. Redmond accepts his offer and is never to be seen by the family again.
