O'Donohoe is the latest member of Ireland's famous 2007 U20 grand slam winning team to join the province, and will join up with Andrew Browne, TJ Anderson, Eoghan Grace and Niall O'Connor in the green of Connacht next season.
He also started for Leinster in Connacht's New Year's Day defeat in the RDS this season. The former Belvedere College man has captained Leinster 'A' this season and has played 19 times for 'A's including eight times in the British and Irish Cup.
"I am delighted to be signing for Connacht next season. I have worked under Eric and Dan in my Ireland U20 days so I have first hand experience of how passionate they are about the club and also how ambitious they are so I am very excited by this challenge," said O'Donohoe.
"I will obviously miss the lads and the back room staff at Leinster as I have been here since my academy days, however Connacht is a new chapter in my rugby career that I am very excited about"
Head coach Eric Elwood added:
"We're delighted Paul is joining us, I've known Paul since he starred for the Ireland U20's in '07 and I believe he's a top class player and very capable of the standard required in the Magners League and European competitions. He's a young dynamic scrumhalf and will fit very nicely into our setup here."