Together with Brendan McFarlane and Pat McGeown, he made an attempt to escape in 1978 dressed as a prison warden, but they were caught before they reached the prison perimeter. That plan having failed to come to fruition, he joined the blanket protest in the Maze's H-Blocks for four years. In September 1983, he helped Brendan McFarlane, Bobby Storey and Gerry Kelly to orchestrate the successful mass escape of 38 republican prisoners from the Maze. It was the largest prison escape in British penal history. According to a BBC documentary about the escape, Marley was the mastermind, having come up with the idea with the aim of embarrassing British Prime Minister Margaret Thatcher, as the Maze was considered to be one of the world's most secure prisons. Marley, unlike his three co-conspirators, did not take part in the break-out as his release date was coming up.