The 22-year-old second row failed to make the breakthrough at senior level and will now now hope to do so with the Ospreys.
He will meet up with his new team-mates when they report back for pre-season training at the Ospreys Llandarcy HQ at the end of June.
McInerney, who can also play in the back row, said: "I'm really excited about signing for the Ospreys and being part of what they are trying to build.
"I can't wait to join up with the squad for the first time next month, the Ospreys are an ambitious organisation with first class facilities, a talented squad and good coaches so it was an easy decision to make.
"I realise that the competition for places there is intense, with British & Irish Lions and Welsh internationals in the second row, but I'm really looking forward to the challenge of establishing myself at the Ospreys over the coming years."
Ospreys Elite Performance Director Andrew Hore added: "We are extremely pleased to have secured Conor's services. Our expanding scouting network has identified him as an outstanding medium-term prospect with the desire and characteristics to be an Osprey.
"He is a robust, hard-nosed and uncompromising player with excellent lineout ability and we have the confidence that with the improvements we have made to our player development programme, we can help him use his natural ability to become a world class lock.
"He wants to be successful and has excellent leadership qualities that will enhance the Ospreys environment. We are looking forward to welcoming him into our set-up next month."