Owen Pattie's emergence in Canberra's starting side has left Tom Starling seeking more regular first-grade opportunities.
The 28-year-old has permission to negotiate with St Helens, where he is understood to have a three-year offer.
His move is expected to happen immediately, although his Raiders contract runs through the end of 2027.
"Tommy's got the all clear to proceed with his St Helens negotiations," Canberra coach Ricky Stuart told the Canberra Times.
Stuart said he understood Starling's position and would not keep him as depth behind Pattie, calling that "the wrong thing to do by the individual."
Starling has made 156 NRL appearances since his 2018 first-grade debut for Newcastle, before establishing himself in Canberra.
At St Helens, he will join fellow Australians Sean O'Sullivan and Christian Tuipulotu.
Kevin Walters, the Kangaroos coach, is due to take charge of the English club in 2027 on a three-year deal.
The move gives Starling a chance to continue his career in Super League while Canberra build around Pattie at hooker.