Jamie Langfield's contract with Aberdeen has been mutually terminated after he fell behind Danny Ward and Scott Brown in their goalkeeping pecking order.
The 35-year-old made 278 appearances for the Dons in 10 seasons, and played in his testimonial against Brighton this summer.
"It was a difficult decision to make but one I believed would benefit me and the club," Langfield said on Twitter.
"I would like to thank every member of staff past and present, from the cleaners to the chairman, who have supported me and my family for the last 10 years.
"I would also like to thank every management and coaching team that have trusted and believed in my ability, and all my team-mates past and present who gave their all for me, and hopefully they felt the same in return."
Langfield is now expected to sign for St Mirren as a player-coach.