He has nine senior caps with the province, including two European appearances against Gloucester during last season's Heineken Cup campaign.
Prior to joining Connacht, the Belfast High School graduate was with the Ulster Academy for two years before turned professional in 2008.
He earned 25 caps for Ulster and has represented Ireland at Schools and 'A' level. McCrea has three Ireland 'A' caps, he was a member of the Plate-winning squad at the 2008 Churchill Cup.
The 6ft 1in, 102kg winger will now link up with Jersey RFC who currently play in the RFU Championship in England.
Connacht team manager Tim Allnutt said: "We'd like to thank Mark for his dedication and hard work at Connacht over the last two seasons. We wish him all the best with Jersey RFC and with his future rugby career."
Meanwhile, the Connacht coaches picked out Willie Faloon, Miah Nikora and Brian Murphy for special praise after the westerners' first win at the Arms Park since 2001.
Flanker Faloon touched down twice in the 26-22 victory away to the Cardiff Blues last Friday with Nikora kicking a late clinching penalty and Murphy enjoying an impressive debut in the centre.
"We know we're very competitive at home. But the challenge for us was to back up the good result of last week (against the Ospreys), and we've done that," said head coach Eric Elwood.
"We haven't won here in 12 years. We put a lot of pressure on the boys this week and they trained really hard. And in fairness they responded well. So it's a good victory. We're really, really pleased.
"Fair dues to Willie. He was out for a long time with a fractured cheekbone. But he was brilliant against the Ospreys and he backed it up again tonight."
Connacht's backs coach Billy Millard, who formerly coached at Cardiff, added: "Credit must be given to Miah (Nikora) and Brian Murphy who came in as late replacements for tonight's game. They both performed like they've been playing next to each other all season.
"Personally, it is a very sweet victory and a nice pay-back after our disappointing loss to the Blues in round 1 of the competition back in September."