The City manager has signed four players in the last week and Keogh joins fellow Irishmen Steve O'Holloran and Roy O'Donovan and Ireland qualified Gary McSheffrey who will all complete moves on Thursday morning.
Speaking about Keogh who joins from Carlisle on a three year deal, Boothroyd told Sky Blue Player: "Richard is another hungry player who comes here looking to prove himself and that's exactly the type of character we want.
"He's already got 170 career appearances under his belt, which is a decent level of experience for a young player, and I'm very much looking forward to working with him."