McMahon, a former player with the club, has left with immediate effect after a little more than two years in the role.
He had worked as head of coaching in the club’s academy system before moving up following Derek Adams’ arrival as manager in November 2019.
Speaking about his decision, McMahon said: “I feel now is the right time for me and for Morecambe to move on and, initially, I am looking to spend some quality time with my family over the Christmas period, before embarking on my next challenge.
“I am incredibly proud to have played a part in the club’s promotion to League One and, along the way, helping to develop and mentor players and coaches in my various roles at the club.
“I wish all at the club, Stephen Robinson, the team and all the fans the very best for the remainder of the season.”
Robinson added: “Firstly, I’d like to thank John for everything he’s done for me since I came to the club.
“He’s been a very good support, especially in the early stages, to myself and Diarmuid (O’Carroll, first-team coach).
“John and I spoke. We felt it was best for everybody that John moved on: he had a contract until the end of the season but we felt it was in everybody’s best interests that we sorted something out now.
“We wish John nothing but the best, he’s a very good coach, a very good guy, and we wish him every success.”
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