The Irishman, who joined the Saddlers in the summer on a season-long loan from Salford, has struggled during his time in the Black Country.
The 30-year-old has only scored once, in the 2-1 defeat away at Swindon on November 2.
He has not featured for Walsall since January 7, missing more than a month with an achilles problem.
The striker has completed a move back to Ireland to join League of Ireland Premier Division side Shamrock Rovers.
The Irish domestic league began on February 14 and clubs can make signings from outside of the division until March 2.
Rovers have won their two opening games of the season.