The winger turned out for ex-club Birmingham with an electronic tag on his ankle after a drink-drive conviction.
Most recently, his career hit the buffers in Spain as Real Zaragoza off-loaded him over his failure to show up on time for training.
Pulis jumped at the opportunity to snap up Pennant, 27, for peanuts in a deadline-day loan deal. But the Stoke boss admitted: "If it was too much money it wouldn't be worth the risk.
"There's a balance you must find and we feel we've struck that in Jermaine."
Pennant's first chance to repay Pulis for his faith comes tonight against Villa.
The Stoke boss added: "The best thing about Jermaine is he has something to prove to a lot of people.
"I'm just hoping we can keep him in check now."