The Blues boss was full of praise for the unique goalscoring threat the Belgian brings to the side.
The Belgian forward has been largely absent from the Blues first team this season, with a series of knocks and a three-game suspension having limited his playing time.
And although he was back in the match day squad for the recent loss to Manchester United, failing to make an appearance from the bench, Martinez has backed him to play a big role in the upcoming games against Arsenal, Norwich City, Sunderland and West Ham United.
"In different moments in your career there are little spells where, for one reason or another, you cannot get any momentum,” he told evertonfc.com.
“But I expect Kevin to discover that momentum and have a massive say in our performances ahead. He was in the squad against Manchester United and he’s a really important player for us; that will never change.”
The Blues boss is also hoping that the Belgian can get his side back among the goals, helping them to overcome the 3-0 loss to the Red Devils.
The Blues were disappointing in the defeat to United, as Romelu Lukaku cut a frustrated figure on his own up front, while their 1-1 draw with Liverpool before the international break saw them fail to find a way past an impressive Simon Mignolet.
And Martinez is hoping Mirallas can turn that around with the 'unique goal scoring threat' he brings to the side.
"He brings a unique goalscoring threat that you always need in your side and he’s going to be very positive,” he added.
“The way he has been working during the international break was impressive and I expect a really good period from him once he gets fully match fit.”