Foster, 22, who spent the last two months of the 2012 season on loan to Hull, has signed a one-year deal with the Bulls after obtaining a release from his contract with Saints by mutual consent.
Cummins said: "Jamie has got some great experience already for such a young man but he's also got to prove a few points here. I think he did that at Hull and he needs to kick on again now.
He added: "It will be hard for him as well, initially, to leave Saints after such a long time but he's got to take the next step in his career, as a lot of our players have had to do."
Foster scored 224 goals and 32 tries in 50 appearances for St Helens after making his debut in 2010, but fell out of favour last season and coincidentally his last appearance for them was in their shock defeat at Bradford in March.
"I am really looking forward to joining the Bulls and working with Francis Cummins," Foster said.
"I know I'm a good player and I know I can score tries and kick goals and I'm looking forward to getting my head down and producing the form that I know I'm capable of.
"Working with new people will be good and hopefully bring out the best in me.
"When I got the opportunity at Hull it was a case of kicking on again and hopefully the same thing can happen again here at Bradford."
Bradford's only other new recruits for 2013 so far are Matty Blythe and Ben Evans, who have joined on loan from Warrington.
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