Previously he rose through the ranks at Blackburn Rovers where he became a regular in the Premier League team's reserve side.
Sutton told BBC Lincolnshire: "O'Keefe is a box to box midfielder whose progress we have been following."
O'Keefe is six feet three inches tall, which Sutton said was crucial: "I think it was important we got some bigger players in."
He added: "I think at the end of the season we were found wanting in certain areas and that was certainly one of them. He has an eye for goal, and we're pleased he's on board."
Source: BBC Sport
Source: BBC Sport