The 'Ted' star realized he needed to turn his life around as a troubled teen growing up in Boston when he was sentenced to two years in prison for assault and attempted murder after beating a stranger, but says the practicality of actually making a change was a daily struggle.
Speaking on ITV's 'Daybreak', Mark confessed: "There were moments where I knew I needed to get on the right course. Very sobering moments. As a 17-year-old adolescent going to jail, that's a very sobering moment.
"I had a very specific moment where I knew I needed to change my life, but when you decide to change your life then actually doing it, that becomes a very challenging and uphill battle that you need to take on a day-to-day basis."
Mark - who was addicted to cocaine by age 13 - immersed himself in his local youth group, the Dorchester Boys and Girls Club and says the support of its programme leader Mike Joyce was the only thing that helped him get back on track.
He added: "Thankfully the people that I did look to as being role models were still there. The guy Mike Joyce who runs the Boys Club, he was our parish priest, those were the heroes I should have looked to. Unfortunately, I was looking to the wrong people for so long for inspiration."
As a result of his tough upbringing, the 'Broken City' actor and his wife Rhea Durham like to spoil their four young children because he wants them to have everything he never had.
Quizzed about becoming a father, he replied: "It's the greatest accomplishment of my life, I have the greatest wife and the most amazing children. But it's also the most demanding role I'll ever play and between that and work I've been very blessed.
"I like to give them all the things I didn't have and I like to make them appreciate that a lot of people are less fortunate."