Stephen Robinson has clinched his first summer signing after the club confirmed Mark O'Hara would join the Buddies.
The former Motherwell and Kilmarnock man signed a pre-contract deal following the expiry of his contract at Fir Park.
The 26-year-old joins Saints on a two-year deal, having made 74 appearances - scoring eight goals - for Motherwell and playing a part in their qualification for Europe.
O'Hara told stmirren.com: "I spoke with the manager and I could just feel that it's going to be something special next season so I'm happy to be a part of that.
"I feel now I'm well experienced and I do have a lot to bring the team. I feel my best football is yet to come and hopefully that will be with St Mirren over the coming seasons.
"The manager sees me as a box-to-box midfielder, getting about the park and affecting both ends of the pitch. But I'm happy to help the team in any way that I can.
"I wish I could just get started right away but I'll enjoy my next couple of weeks and I'm really relishing the challenge coming in here."
