McGrath has previously worked for AFC Wimbledon, Charlton Athletic, Sheffield Wednesday and Newcastle Thunder Rugby League club.
He will work alongside Graeme Lee and Micky Nelson overseeing the strength and conditioning, development and nutrition of the first team players.
McGrath said: “I am delighted to be here at Hartlepool United.
"I’ve called Hartlepool home now for the past eight months and now to be working for its historic club and its fans, I’m delighted.
"The gaffer, Michael Nelson, Tony Sweeney and all the staff have made me feel very welcome and I want to give it my all to help the gaffer and the club move forward.”
Lee added: “We are very pleased to get Keith in so quickly after the departure of Jake Simpson.
"Keith comes from a good footballing background and has picked up experience at some highly established clubs like Sheffield Wednesday.
"He is already showing he will be a great asset to this football club."