McCarthy has endured a tough period over the past six months as he has adapted to life at a new club and also faced tough work getting ready for the Premier league.
His display against Hull City was enough evidence to convince Martinez that the 19 year old is ready for the first team.
Martinez said: "He showed on Saturday [against Hull] that he is ready. We all know James is going to be a big star in world football. He has been working very hard and lately you could see he was ready in training and on Saturday he showed that he was ready to enjoy his football and ready to win games for Wigan.
"When you get frustrated it is because you are ready to play. Sometimes you get a big move into the Premier League and with the change of environment it is very different and sometimes you lose the focus on your game. "It was a big move for him as a young man when he came down from Scotland as it was the first time he had moved away from his only club and that takes time. "It is important we help the youngsters - and every player that comes to Wigan. James has had the period he needed to settle in and now he is ready to play football and enjoy it. When he does that I'm sure the fans will enjoy it too." McCarthy is now in line for a starting position against Wolves on Saturday.