After seven years with home club Auckland, hooker McCartney has opted to make the move to Ireland, arriving earlier this month after the conclusion of New Zealand ITM Cup season.
The 28-year-old can play at both hooker and prop and is already a familiar face to Connacht head coach Lam, having been handed his first start by the New Zealander seven years ago.
Lam has opted to name him on the bench for Friday night's GUINNESS PRO12 home clash against Zebre - although former All Blacks full-back Mils Muliaina does start on his debut with centre Bundee Aki also making his home bow.
And McCartney insists the new arrivals are intent on helping the Irish side, currently sixth in the table, maintain their strong start to the season.
"Coming to Connacht, it's a club that's on the rise. They've got aspirations to be making the top six, really competing in this league. That in itself was really exciting," McCartney told Connacht's official website.
"I've obviously worked under Pat before and I really enjoy his coaching philosophy. He gave me my first start for Auckland back in 2007 and really, I owe a lot of my career achievements to him from those early days.
"When he told me on the vision, a few of the guys I knew were already here too, so it's an easy decision.
"I just want to come over here and fit into the team and do everything I can to make sure Connacht win.
"The new guys I've spoken to, they've got the same vision. They're not just here to play a bit at the end of their careers, we're here to win. That's the aim."
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