An Irish rogue wins the heart of a rich widow and assumes her dead husband's aristocratic position in 18th-century England.
The rise and fall of the adult life of Irishman Redmond Barry (Ryan O'Neal), who, in his later life, would be known as Barry Lyndon, from the mid to late eighteenth century, is presented. Growing up in humble means, largely due to the early death of his aspiring lawyer father, the potential family breadwinner, Barry strives to live up to the standards of being a gentleman in every respect of the word, including monetarily. He leads a disjointed early adult life in trying to find his way, sometimes being unfairly given some hard knocks as the ways of the world work around him. He seems to find his stride in falling in love with wealthy and married Lady Lyndon (Marisa Berenson), who he ends up marrying following the death of her elderly first husband, Sir Charles Lyndon (Frank Middlemass). In taking over the affairs of the Lyndon mansion, Barry is able to live a means of his liking, all off the Lyndon's now quickly dwindling wealth due to Barry's squandering. As Barry is without money of his own, Mrs. Barry (Marie Kean) encourages her son to work toward a peerage as a means to have money of his own, as she fears that if Lady Lyndon were to die, she would leave all of what would remain of the Lyndon wealth to her son, Barry's stepson, Lord Bullingdon (Leon Vitali), with whom Barry has always had an antagonistic relationship to the point of Lord Bullingdon wanting revenge on the woes that his stepfather has created in their lives. Outwardly, Lord Bullingdon may seem to be the cause of Barry's fall, however, it may be more attributed to Barry being unable to adapt to any of the lives into which he is thrust to truly reach his goal of being a gentleman.