The 21-year-old scrum-half has not missed a game for Connacht since Lam’s predecessor Eric Elwood handed the Loughrea talent his debut 14 months ago, making him the only ever present player in the RaboDirect Pro12 last season.
Marmion’s signature on a new deal will lift morale in his struggling side after Saturday’s league defeat at home to Glasgow kept them rooted to the foot of the table.
“I’m delighted for Kieran and for Connacht Rugby that we have this new deal,” Lam said. “Kieran is a fantastic player and a key member of our squad and it’s a real boost that he sees his continued development and future with the club he started his professional career with.
“From day one, Kieran has impressed me with his attitude, work ethic and incredible maturity and I have no doubt that he will go on to achieve great things within Connacht and Irish rugby.”