Born and raised in Sydney, Alaalatoa has been capped five times for Samoa, with his last game for the country coming in their 2019 Rugby World Cup pool stage defeat to Ireland.
He made his Super Rugby debut for the Waratahs in 2014 and moved to the Crusaders in 2016. He has since played 89 times for the club and won three Super Rugby titles as well as last year’s Super Rugby Aotearoa championship.
“It is a huge honour to be given the opportunity to join Leinster Rugby,” Alaalatoa said.
“They have enjoyed a lot of success for a long time and have produced a lot of Irish internationals which speaks highly of their rugby programme and team culture.
“It is something that I am really excited about being a part of and I am looking forward to starting a new adventure in Dublin with my family.”
Head coach Leo Cullen added: “We are very excited by Michael’s arrival in the coming months. He is a player with top quality Super Rugby and international experience and he is hungry for further success and to play a part in building on the work that is already underway here.
“We have a group of younger props who will only benefit from his experience and we believe the wider group will also learn a lot from Michael and his rugby knowledge from playing with the Crusaders in particular.
“We look forward to welcoming him and his family to the club later this summer.”
Crusaders head coach Scott Robertson said: “Mike has left his mark on our team, our culture and our scrum. He is a true professional who gets the best out of himself, and continues to get better.
“He’ll leave our team as a world class prop, and we’ll miss him, Kara and Parker, but we are determined to send him off on a successful note at the end of the 2021 season.”
The 6’3″, 126kg tighthead will provide Ireland internationals Tadhg Furlong and Andrew Porter with extra competition at Leinster.
Vakh Abdaladze is also in the mix for gametime at tighthead having recently returned from a long-term injury lay-off, while veteran prop Michael Bent is expected to move on at the end of the current campaign. Academy prop Tom Clarkson has also gained first team experience this season.