In November 2010, Mercer joined the Halifax Rainmen as a non-contracted training camp invite. He helped the team go 3–1 over four preseason games between December 10 and 19, and made his regular season debut for the club in the season opener on January 2, 2011, scoring 14 points in a 109–99 win over the Vermont Frost Heaves. Mercer left the team on February 15 because of undisclosed family reasons. Team Owner Andre Levingston said Mercer returned to Atlanta to be with his wife and young child. His departure left a gaping hole at the Rainmen's two spot, where Mercer averaged 14.5 points per game, second on the team and 15th in the Premier Basketball League.