Rooney, 22, has most recently enjoyed loan spells with Burton and Rotherham and will be available for Tuesday's League Cup tie with Cheltenham, having signed on loan until January.
"It's a fresh start for me and I can't wait to get started," he told the club's official website.
"I have really enjoyed the training so far and I like the way Richie Barker sets his team up to play good football. The lads have been really welcoming and I've been really impressed by the set-up at the club.
"I'm probably a little bit behind the others in terms of match fitness but that will come and then I hope Crawley supporters will see the best of me."