The Wales Under-21 striker was without a club having been released following Saints' promotion to the Premier League.
"I'm at a stage now where I need to go and play games consecutively and I feel ready for it," said the 21-year-old. "I'm itching to get going.
"I've been at Southampton since I was 11 so I was there 10 years and enjoyed my time but I'm happy to move on. I hope to push for a first-team place and play regularly."