Foster will join up with the Airlie Birds as they aim to bounce back from their defeat to Catalan at the weekend.
Foster has been out of favour for St Helens, after several blunders under ex-coach Royce Simmons saw the 22-year old dropped from the first team squad. He will be available for selection ahead of Hull FC’s derby match on Monday night against Hull KR.
Hull FC coach Peter Gentle said: “With Ben Crooks facing surgery which we couldn’t delay any longer, we felt it was important to try and bring somebody in with the deadline approaching and to land a player of Jamie’s calibre is a real coup.
“He had a fantastic season last year for Saints scoring plenty of tries as well as being an accomplished goal kicker so he certainly fits the bill.
“He is a talented youngster with pace and an eye for a try and he comes here with a point to prove so we look forward to seeing him in the Black and White of Hull.”