St Mirren are moving to a new stadium

He replaces Gordon Scott, who had temporarily been performing the role as operations director.

Caldwell said: "I actually had a bad time over the way I left Ayr United. It kind of soured it all for me.

"After giving the club everything for 10 years, I was made redundant on the week I was going to get married."

Caldwell admitted he had doubts about returning to the game.

"But, obviously, when St Mirren came to me and asked if I would be interested in the post, I said yes," he told the club website.

"St Mirren are obviously a big club and have the potential to be even bigger.

"The directors have done magnificently well by running the club and their own businesses side by side.

"But I think they felt it was time to bring in someone on a full-time basis to deal with everything ongoing."

Scott said he would continue to be involved with the club, particularly the move to their new stadium and a planned new training facility.

Meanwhile, Mark Corcoran, Ryan McCay and Stewart Kean, with a penalty, were on target as St Mirren secured a comfortable 3-0 win in their pre-season friendly away to Stirling Albion.