Charnley, 21, was Super League‘s top try scorer in 2012, scoring 36 tries in all competitions, and has signed a new four-year deal.
Captain O’Loughlin’s new two-year deal includes a further one year option which could see him join the Warriors coaching staff.
Hooker McIlorum has agreed a three-year extension, plus a further option for 2016.
Head Coach Shaun Wane said: “To say I am pleased to have secured the services of these three players would be a massive understatement. Josh, Lockers and Mickey are part of the back bone of this great Club. Like me, these players have a great desire to make Wigan clearly the greatest club in the world again.”
O’Loughlin’s next appearance for the Warriors will be his 300th, and he enjoyed his testimonial year with the club in 2012.
He said: “I am thrilled to have signed a new deal with the club and am looking forward to the next couple of years as a player before having the wonderful opportunity to join the backroom staff.
“I can’t believe it’s ten years since I made my first team debut in 2002. I have enjoyed every minute of it and could never imagine playing for anyone other than my hometown club.”