Adams has appointed McMahon as his assistant boss while club skipper Roche has agreed to a dual role as player and goalkeeping coach.
McMahon is a former Shrimps player who has been working with the club’s academy system for the past couple of seasons and is a highly-rated and experienced coach.
After hanging up his boots, McMahon spent eight years on the coaching staff at Tranmere Rovers, during which time he had two spells as caretaker manager in the 2003–04 season and at the end of the 2005–06 season.
He moved to become first-team coach at Shrewsbury Town in June 2006 and was made assistant manager in September 2007 before joining Liverpool as reserve team coach in 2009.
In June 2011, he rejoined the coaching staff at Tranmere as first-team coach and had another spell as caretaker manager of the club in February 2014.
Speaking of the appointments, Adams said: “I’m delighted that John and Barry have agreed to take on the responsibilities of assistant manager and goalkeeper coach.
“Both have excellent knowledge of the players at the football club and at league level.
“During my first two weeks at Morecambe FC I have been impressed with their work ethic and desire to move the Shrimps forward.”
McMahon, who aided Roche and Kevin Ellison during their recent spell as caretaker managers, added: “I know the players and their capabilities and I think it has been mentioned before that I believe we’ve underachieved in games.
“I feel my strengths are on the training ground working with people, both players and staff.
“I’m not frightened or fearful of a challenge with new and different people. I’ve not known the manager for long but I’ve seen lots of positives in his sessions and handling of staff and players.
“I’m excited for what the future holds and I hope we can develop positive relationships and environments for the club going forward.”