The pair, who enjoyed huge success in the League of Ireland previously with Cork City, were released as part of a clearout at English League One Hartlepool United at the end of last season, and have been free agents since.
Limerick have benefited from the support of McManus and are reaping the rewards. Pat O’Sullivan, club chairman, stated: “I am delighted such high profile players see the potential this club has to be a huge success.”
Behan, 27, from Abbeyfeale, is a former Ireland U21 international, but has endured a tough time with injury.
Gamble, from Togher in Cork, joined Hartlepool in January 2010 and has represented Ireland twice at senior level. Limerick currently lie fourth in the First Division — two points behind second-placed Cork City, six points behind leaders Shels.
Limerick face Wexford at Ferrycarrig Park tonight while Cork City host Waterford.
O’Sullivan also revealed ambitious plans for the development of the Markets Field for the 2012 season “as a home for senior soccer in Limerick, which we have now been able to do due to the kind support of JP and Noreen McManus and the LEDP (Limerick Enterpirse Development Partnership)”.