"I would like to express my sincere thanks on behalf of the board for Barry's valuable contribution as a non-executive director over the last seven years," said Charles Scott, the bookmaker's chairman, in a company statement.
Gibson formerly served as a group chief executive for Littlewoods, a group retail director for BAA and as a non-executive director for Limelight and Somerfield.
According to William Hill's corporate Web site, Gibson currently is the director of National Express Group and Homeserve. The sports betting company did not disclose further details on his departure.