The back-row earned his first two Lions caps in Australia last year, starting in the third Test as the Lions wrapped up their first tour victory in 16 years in emphatic style.
And O'Brien, who was in demand by some of Europe's top clubs, wants to back up last summer's success by continuing to impress on both the domestic and international stage
"It is flattering to find yourself the subject of interest from some of the biggest rugby clubs in the world, but in the end I made a decision based on the standard mix of professional and personal considerations," said the Irishman.
"It was a very difficult decision but, with a World Cup next year and the fact that I believe Leinster can continue to win trophies, I have decided to commit my immediate future to the club.
"I am very excited about what Ireland can achieve under Joe Schmidt and I am confident that, under Matt O'Connor, Leinster will remain the power in Europe it has been over the past five or six years."