The 28-year-old combines the Buddies following the expiry of his contract in fellow Scottish Premiership side Motherwell
Talking to stmirren.com concerning the prior Wycombe Blackpool Crawley and Oldham player, manager Jim Goodwin said:"I am delighted to finally get Charles over the line.
"It is one we've been working on for a number of weeks now. He's had a number of other options on the desk but I am thrilled he sees his future here at St Mirren.
"He has pace, he has power, he is great on the ball, he matches the way we would like to play and he's a really good character as well.
"People might look at the last 12 months or so with all the absence of game time he's needed and that's solely down to a little bad luck on the injury .
"But he's completely recovered now and he's done a thorough health care with our physio, Kevin Bain, so there's absolutely no concerns with Charles' fitness going forward."