The 27 year old joined the Connacht Academy in 2011 and since his arrival in the Sportsground has played over 160 games for the province. Marmion’s outstanding form during his time with Connacht has led to him being capped 27 times for Ireland since making his debut against Argentina in 2014.
His international representation began in his teens when he played for Ireland at Under 18, 19 and 20 level.
Commenting on the signing, Connacht Head Coach Andy Friend said: “Kieran has been an outstanding player for Connacht and for Ireland. He is a diligent professional and through his hard work he has progressed through the Connacht Academy and on to play for Ireland. His progress demonstrates the support that is available to players through our academy pathway. Kieran’s commitment to Connacht for a further three seasons demonstrates his ambition to contribute at provincial and international level in the coming years. His signing also ensures that we continue to retain a squad equipped to compete at the highest level of European club rugby”.