O'Leary's contract with employers Luton Town is due to end in the summer and he is not expected to be given a new contract by last seasons League One winners.
O'Leary, who was represent The Republic of Ireland at nearly every age level, arrived at Tranmere for one month in October and then returned in Janiary until the end of the season on-loan.
To date he has started 16 games, made two substitute appearences and scored three goals against Gillingham (1-1), Chesterfield (4-1) and Port Vale (3-0) and picked up three yellow cards.