The ex-Warrington Wolves hooker, 38, joined in January having previously been an assistant at Catalans Dragons.
However, after nine years in Europe, Monaghan has decided to head back. He said: “I’ve loved my time here at Wakefield.
“I’m sad to be leaving but my wife has been offered a job over in Australia.
“We sat down as a family and realised that it would be the perfect time to return home.
“It is weird. If you had asked me at the start of the season if I’d be staying at Wakefield for the next few seasons then I’d have jumped at the chance but circumstances change.”
Monaghan, who won the Lance Todd Trophy in Warrington’s 2009 Challenge Cup final victory over Huddersfield Giants, added: “Wakefield are a great club and everyone has been amazing. It has been a real eye-opener for me, to have been at Warrington and Catalans who can bring in any player and who have big grounds to then come here and see what an exceptional job the coaching staff, players and club as a whole do.
“It is fantastic to see and it is great to see that the competition now takes notice of this.”
Trinity head coach Chris Chester added: “It has been a pleasure working with Mick over the last 12 months.
“He’s added a lot of expertise and myself, the rest of the staff and playing group have learnt a lot off him so he’ll be missed.”