The 22-year-old signed a long-term deal with the Merseyside club to seal a reunion with manager Roberto Martinez, who left Wigan at the end of last season.
But with the Premier League side also clinching a number of other high-profile players in the window - including loan deals for Gareth Barry and Romelu Lukaku - McCarthy knows that he will have to bide his time to make an impact.
"I am looking forward to trying to prove why I am here," he said.
"It is not going to be easy, we have got a lot of competition for places. I am going to give it my best shot and hopefully I can do well.
"There are a lot of big names here. If I need to bide my time, I will bide my time."
"It is great to be here with him and hopefully I can stamp my authority on the team and get as many starts under my belt as possible," he added.
