The 33 year old Leinster and Ireland back row says it's been on his mind for a while and the decision hasn't been taken lightly.
Jennings enjoyed a successful spell at Leicester earlier in his career winning a Premiership title.
Staying with rugby and several of the extended Six Nations squad have been selected in Leinster’s starting 15 for tomorrow’s Guinness Pro 12 clash with Zebre at the RDS.
Marty Moore is at tight head while Fergus Mc Fadden, Gordon D'Arcy, Luke Fitzgerald and Eoin Reddan are in the backs.
Cian Healy is on the bench along with Sean Cronin, Isaac Boss and Dave Kearney.
Iain Henderson starts in the second row for Ulster ahead of their clash with Edinburgh in Murrayfield.
Robbie Diack misses out after picking up a knock in training.
Ulster are fourth in the table, 2 points ahead of Leinster.
