Dublin-born Tony joined Liverpool from Irish club Dundalk, for whom he had made his debut at the tender age of 19. He was the joint-winner of the P.F.A.I. Young Player of the Year award for the 1989/90 season and signed for Liverpool shortly afterwards. Injury reduced his chances of making a big breakthrough at Anfield and after three seasons without a first-team appearance for Liverpool, he was released on a free transfer and returned to his native Ireland in the summer.

In the summer of 1996 Cousins moved to his home city to play for Shamrock Rovers and enjoyed six seasons with the Hoops, during which he scored 46 times in 145 league matches. After leaving Shamrock, he had a single season at Bray Wanderers before announcing his retirement as a player. However, Cousins stayed in the game and returned to Shamrock as their Under-21 manager before becoming assistant manager in 2003, a position he also took at Drogheda United. In 2006 Tony Cousins finally became a manager in his own right when he took over the job at Galway United. He was appointed Longford Town manager in December 2009 and resigned as manager in August 2016 after 209 league games in charge.