The 27 year old has played rugby union in the past and will provide options for Matt O'Connor in the centre.
Te'o, who has played with the West Tigers and the Brisbane Broncos in the past and was selected in this year's State of Origin three game series with Queensland, will mark a significant career milestone this Thursday when he lines out for his 150th National Rugby League (NRL) appearance against the Brisbane Broncos.
Born in New Zealand, he made his senior international debut with Samoa in the 2008 Rugby League World Cup against France scoring two tries.
He will join Leinster Rugby once his season with the Rabbitohs concludes and ahead of his arrival Te'o spoke to leinsterrugby.ie, "This is a great step for me personally and is just the type of challenge that I was looking for at this stage in my career. Leinster is one of the leading lights of Northern Hemisphere rugby and the opportunity to return to union was also an opportunity too good to pass.
"It was a difficult decision to leave the Souths and league in general but I have taken my time over this decision and I believe that what Matt O'Connor and the coaching team have cultivated in Leinster is something special and I look forward to getting stuck in."
With the NRL season still to reach its conclusion, Te'o will not be joining his new teammates until after his commitments with the Rabbitohs have been completed.
"There is a lot of footy still to be played in this season and I owe it to Michael Maguire, his staff, and the rest of the players and of course the South' Members and fans to focus all of my attention on those games starting this Thursday against the Broncos. There will be a time for farewells and thank yous when all is said and done."
Leinster Coach Matt O'Connor welcomed the signing and looked forward to his arrival.
"Ben is someone that we have taken an active interest in for some time now in particular as he made his intentions to change codes some time ago. I was home during the summer and met with him a number of times. He is keen and eager to make a lasting impression at Leinster and to develop into a world class rugby player.
"He has been a great professional in all of the clubs that he has played with and he has all the physical attributes to compete and deliver for Leinster. His presence will give us a different dynamic in the midfield. Once he arrives, we will have a player at our disposal for the whole season to augment what is already an exciting array of options for the year ahead."
The lack of recent rugby union experience will not be too big an obstacle either according to O'Connor.
"It is something that I dealt with myself as a player but with his professionalism, his physicality and his skill set, there is no reason why the transition can't be a success. Both codes are littered with examples of players that have made the transition and I look forward to working directly with Ben when he arrives.
"He is a dynamic and explosive ball carrier and that physicality will enhance our offering both in attack and in our defence. I think the Leinster supporters are going to like what they see. I know we in the Leinster coaching team are looking forward to his arrival and the younger players will learn a lot from him. He has the character and the application to be a success at Leinster Rugby."
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