Continuity mistake: Barry is introduced to Gustavas Adolphis, the 13th Earl of Wendover, by Lord Hallam, to help him obtain a title. In the receiving line to meet Your Majesty, another man is introduced as Lord Neville, yet later when Barry is eating in a restaurant and runs into the 13th Earl of Wendover, he calls him Lord Neville. It seems his name should be either Lord Wendover, as he was called previously, or Lord Adolphis, as we learned that his real name was from Lord Hallam.
Continuity mistake: When Lord Bullingdon and Barry Jr. are left behind by the chaplain while at their lessons, Lord B. is copying a text. The various shots showing his writing seem to be in the wrong order: in some shots there is a line of writing less than in the previous shot.
Continuity mistake: Barry Lyndon bloodies Mr. Toole's face in a boxing match. The blood disappears in the next shot.
Continuity mistake: In the scene when Barry interrupts the meeting of Nora and Captain Quin, the direction of the light source changes several times, indicating repeat takes.
Continuity mistake: After joining the British army, Barry is in a bare knuckle fight. Part way though the fight, the ribbon tied around his hair is loose, but as the fight ends, it is neatly tied up again.