In response to a report within the Each day File, the Scotland worldwide has been granted permission to talk to the Buddies a couple of transfer to Paisley.
The Saints are understood to have provided 31-year-old Gallagher a two-year deal. He has 12 months remaining on his Dons contract.
Aberdeen defender Declan Gallagher has emerged as a switch goal for fellow Scottish Premiership aspect St Mirren.
The Dons have already bolstered their central defensive choices throughout the summer season switch window by recruiting Celtic defender Liam Scales on a season-long mortgage and Wycombe Wanderers centre-half Anthony Stewart on a two-year deal.
Gallagher made 31 appearances for the Dons final season and began 16 league video games.
The previous Motherwell defender has been capped 10 instances by Scotland.