Williams was selected for this summer’s British and Irish Lions tour, but having impressed in a pre-tour warm-up match against Argentina, he was forced to return home after suffering a hamstring injury in the first game on Australian soil against Western Force, having scored two tries.
His departure from Kingsholm will come just as his Wales team-mates Jac Morgan and Dewi Lake join the west country club from Ospreys for 2025-26.
“Tomos Williams will depart Gloucester Rugby at the end of the 2025-26 season,” a statement on 16 December had said.
“After impressing at Kingsholm, Williams was offered a new deal to stay at the club beyond the end of the season, but has instead opted to pursue a new challenge elsewhere.
“The Welshman will depart with the best wishes of everyone at the club when the time comes, but in the meantime, is entirely dedicated to ending his time at Gloucester Rugby on a high.”
Gloucester also announced at the same time that former academy graduate Dan Robson, 33, is to return to Kingsholm next season, 10 years on from his departure in 2015.
The scrum-half previously made 80 appearances for Gloucester, where he started his senior career, before leaving for Wasps and spent seven years there until their demise in 2022. He has been with French Top 14 club Pau for the last three seasons.