The 26-year-old left-back, who spent time at Rochdale and Port Vale before making the move to McDiarmid Park in 2017, is Jim Goodwin’s fourth summer signing for the Buddies following the arrivals of Charles Dunne, Greg Kiltie, and Curtis Main.
The Paisley outfit could bring in at least two more signings as Goodwin looks to get his squad for the 2021/22 campaign sorted as early as possible.
Tanser made more than 130 appearances for St Johnstone and was part of the squad to lift both the Scottish Cup and League Cup last term, although he was left out of the starting line-up for both finals with Callum Davidson opting for Callum Booth.
Tanser and St Johnstone did hold talks earlier this year but Davidson conceded in March that the player was likely to move on, with clubs in England said to be keeping tabs on the left-sided player.
The Blackpool-born player spent time as a youth with Blackpool, Burnley, and Rochdale, before making his senior debut for the Dale as a 19-year-old in April 2013.
Tanser's versatility makes him an ideal fit for the wingback role given Goodwin’s preference for playing a back three and he could well fill the role on the left made vacant by Ilkay Durmus’ exit. He is also equally comfortable in a back four.
The deal is for an initial 12 months with the option of a further year included.