The 24-year-old left Bury at the end of last season after failing to renew his contract at Gigg Lane.
"Lewis gives us something different. He's quick and can play on either flank and even up front," Crawley boss John Gregory told the club's official website.
"We think he's got a lot to offer and it's our job to create the right environment for him to flourish."
Young's arrival at Crawley means that the League One club has signed 11 new players this summer.