St Mirren have signed Graham Carey on a two-year contract after Celtic allowed the wing-back to leave despite having a year left of his current deal.
The 22-year-old Republic of Ireland Under-21 cap had come through the Celtic youth system and had a loan spell with the Buddies in 2010.
Buddies boss Danny Lennon said: "We are very thankful for Celtic in their part, as we are to Graham's agent who also played a big part.
"And our own chairman Stewart Gilmour."
Carey only made one first-team appearance for Celtic and was allowed to leave by manager Neil Lennon following negotiations with their Scottish Premier League rivals.
But Lennon is hoping that the versatile left-sided player will recapture the quality he showed during his loan spell at St Mirren Park.
"He is left sided, which gives us the necessary balance," the Buddies boss told his club website.
"Graham has cut the cord with a big club in Celtic, so it shows you the progression that St Mirren Football Club are trying to make.
"I think the facilities that we have here and the quality of the signings to date were influential in Graham coming here as he did have one or two other things in the line."
Paul McGowan had already made the switch from Celtic earlier this summer, while fellow forwards Steven Thompson and Nigel Hasselbaink had arrived after leaving Burnley and Hamilton Accies respectively.
Meanwhile, Scotland winger Gary Teale was snapped up after exiting Sheffield Wednesday, while goalkeeper Graeme Smith signed for the Paisley outfit after parting with St Johnstone.
Carey had a loan spell with Bohemians before his first spell with St Mirren and most recently was farmed out to Huddersfield Town.
He impressed sufficiently for the League One promotion hopeful's manager, Lee Clark, to attempt to extend his loan in January, but no agreement could be reached.
Carey said: "When I was here the first time, I thought St Mirren were a really good club to be at.
"With the new stadium and training ground, St Mirren are a side who are on the up.
"The other signings over the summer have added a lot of quality to the side and I definitely think that we have a good chance of pushing towards top six this season and hopefully we can do that.
"The biggest difference since I was last here at St Mirren is the quality of the squad.
"It is certainly smaller than two seasons ago, but it looks to me like there is more quality in it."