Strengthening continues for Pat Scully's side as they prepare for next week's kick off in the Airtricity First Division
Foley, 35, is a former Ireland international who won six caps under Mick McCarthy and joins from Belgian side Cercle Brugge after spending three seasons there. The veteran striker also enjoyed spells with Wolves, Watford, Braga, Bohemians and Gent.
O'Brien, 32, is a winger who featured in Cork City's promotion campaign last season and has also played for St Patrick's Athletic and Galway United.
Pat O'Sullivan, the Limerick chairman, said at the unveiling on Wednesday: “I would like to welcome both Dominic and Derek to Limerick FC and am delighted that, once again Limerick FC has been able to attract players of such high quality and profile to the club despite interest in both players from numerous other clubs.
"Both players have seen the potential that this club has to be a huge success both on the field and off the field and will start training immediately as the new season kicks off in less than two weeks time. Pat Scully has pulled together a squad with some very experienced players mixed with some exciting young talent for the coming season and we are delighted that we can now add both Dominic and Derek to this squad.”