Although his commitments with Connacht and Ireland mean the 27-year-old openside is unlikely to make an on-field appearance for Corinthians, O'Connor's signing is a considerable boost as the Cloonacauneen-based club celebrate their 75th anniversary this year.
Corinthians play in Division Three of the AIB League - they finished 11th in last season's table.
Connacht Rugby CEO Gerry Kelly said: "Johnny has made it clear that he wants to give something back to Corinthians if he can. He has always been indebted to Corinthians for what they did for him and it is great to see that loyalty in this day and age."
Connacht's pre-season training has already begun but former Wasps favourite O'Connor is not due to start his pre-season stint with the westerners until next month.
The same applies for Gavin Duffy, who was capped twice on Ireland's summer tour to Argentina, and the rest of Connacht's Ireland 'A' squad members - John Fogarty, Andrew Farley, John Muldoon, David Gannon, John Lyne, John Hearty and Daniel Riordan.