McCarthy sealed a £13 million move from the DW Stadium, following Martinez to Goodison Park, and he has impressed during their rise to fifth in the Premier League table.
The 23-year-old has made 20 appearances this season, and has formed a solid partnership with Gareth Barry in midfield and his manager believes his impact sometimes can go unnoticed.
"James is one of those players you sometimes don't appreciate but he's always there making sure the team has the right balance and what it needs," Martinez told The Liverpool Echo.
"He allows others to shine. He can adapt to different situations during a game when you need him to because of the tactical awareness that he has.
"James never plays according to his age because of the incredible amount of experience he already has at 23."
Everton travel to Tottenham on Sunday and a win could put them four points clear of the London club in the race for fourth in the Premier League.