Redmond Barry (Ryan O'Neal) is a young, Irish farm boy who is in love with his cousin Nora Brady. Despite their mutual affection and under the pressure of Nora's family, she decides to marry the British Army Captain John Quin. Enraged by her decision he challenges Quin to a duel and shoots him. Fearing prosecution he sets out for Dublin but falls victim to robbery on the way there. Pennyless and homeless he sees no other alternative but to join the British Army and is sent to mainland Europe to fight alongside their Prussian allies against France and her allies in the Seven Years' War (1756–1763). Deeply unhappy with the situation he finds himself in, he decides to desert when a chance arises but is later caught out by the Prussian Capatin Plotzdorf (Hardy Krüger), who forces him to either join the Prussian Army or be executed. During a battle against the French he saves the life of his new commander and gains his trust. After numerous acts of bravery during the course of the war he is selected by Plotzdorf and his superiors to spy on the Austrian ambassador Chevalier, who they believe spies for the French and is of Irish origin.
Redmond does their bidding but once he encounters the gentle aritocrat he is overcome with emotion and finds it impossible to betray a fellow country-man, so he confides in him.
The Chevalier and Barry travel the courts of Europe and engage in fixed gambling events in order to sustain themselves. During one of those events he encounters the Lady Lyndon (Marisa Berenson), who is married to an old, ailing and very wealthy man and is the mother of the young Lord Bullingdon. He seizes the opportunity to befriend her and she falls in love with him. A year after Lord Lyndon's death they marry and Redmond assumes the name Barry Lyndon.

Instead of being a loving husband and competent manager of the family fortune, he commits acts of adultery and gambles away the wealth of the family. After the birth of their son Bryan Patrick Lyndon he more and more despises the young Lord Bullingdon, because in the event of Lady Lyndon's death the whole family fortune would go to him instead of Barry. So he tries to bribe the establishment in order to have a title bestowed on him and becomes ever more abusive to Lord Bullingdon, who always hated his stepfather, and further fuels his hatred which would come back to haunt him.
Too late Barry realizes how his actions set a chain of events in motion that would ultimately lead to his demise.

Barry Lyndon is the third and last of Kubrick's epics (Spartacus, 2001 - A Space Oddyssey) but by no means the worst. It is rarely mentioned alongside his other accomplishments like Dr Strangelove or Full Metal Jacket, begging the question why?
Critics loved it and it received four Oscars despite disappointing results at the box office. Kubrick's skill in directing and his trademark camera work turn almost every frame of this movie into a visual masterpiece. The music creates a tense and dramatic atmosphere, first and foremost the haunting melody of Georg Friedrich Händel's Sarabande.
The focus of the movie is the development of the character of Barry Lyndon, from a simple farm-boy to a wealthy and appaling con-artist. It may well be this focus, the fact it is 184 minutes long and the era the movie is set in, that could not capture the imagination of a wider audience. However, if you watch this movie open-minded, you are likely to encounter a cineastic masterpiece by one of the titans of the movie-industry who made an immeasurable impact on film-making.