The 23-year-old has become St Mirren manager Danny Lennon’s ninth signing of the summer.
Lennon told the club’s official website: “Looking at how Sean has come in and handled himself during the pre-season, he certainly deserves his deal.
“I have no doubt that he will be a very good addition to the squad.
“He left Hibs to join John Hughes at Falkirk to get an opportunity but he ended up being part of a cost-cutting exercise at the end of last season.
“Sean has had a few knock-backs but hopefully, having a chance to settle here, he will kick on again.”
