“I’ve had a fantastic year here at Worcester, it’s something I’m really proud of and will look back with a lot of fond memories.
“The fact that this year will be my lasting memory of professional sport as a player is seriously special.”
Williams is the son of former Wales and British and Irish Lions scrum-half Brynmor, and like his father played the bulk of his club career for Cardiff. Williams’ brother Tom also played professionally.
After making his Cardiff debut against Leinster in 2010 as a 21-year-old, Williams went on to make 261 appearances for the Blue and Blacks, bagging 42 tries in the process.
While at Cardiff, he won the European Challenge Cup in 2018 as well as captaining the side on several occasions.
Williams was one of seven Wales internationals to leave Cardiff after the end of the 2022-23 season, joining Ealing Trailfinders for two seasons before finishing his career with Worcester Warriors.
Worcester play his former club Ealing on Saturday in the Elior Champ Rugby semi-finals.