The 24 year-old forward has earned a contract at the Championship One club after a successful trial period at the club.
Williams has been recently plying his trade in University rugby league in Leicester after having come through the ranks at Sheffield Eagles, and is straight into Doncaster’s 19-man squad to face York City Knights this weekend.
“I’m very please, I get along with all the lads really well, pre-season was really good, along with the start to the campaign,” Williams told the club’s official website.
“I signed at Sheffield when I was 16 and spent five years there and got a couple of first team games and it was a really good experience, but I felt I needed a new challenge and got the opportunity to go down to Leicester.
“I just want to get out there playing some games now, I can bring impact, a quick play the ball and I am an all-round team player.”