Gerry Adams has said the Sinn Fein brand is strong enough in west Belfast to retain its Westminster and assembly seats without him.
Mr Adams announced on Sunday he would be stepping down as both an MP and MLA to stand for the Irish parliament in the next general election.
His successor in the assembly will be former IRA hunger striker Pat Sheehan.
Mr Adams will remain as West Belfast MP until the Irish election when he will stand in the Louth constituency.
Mr Sheehan was picked by the party at a selection convention in the Irish Republican Felons clubrooms on Tuesday evening and will be sworn in at the assembly within days.
Addressing party members, Mr Adams said: "We have no reason to fear anything - the people in this room have nothing to fear.
"It's a challenge, we'll meet the challenge so let's make a stand, let's do it together."
Mr Sheehan was first jailed at the age of 19, and shortly after his release in 1987, he was imprisoned again for 24 years for bombing offences.
While in prison, he earned a first-class honours degree in politics and philosophy before being released under the terms of the Good Friday Agreement.
He was married to the late republican Siobhan O'Hanlon and has one son.
For next May's assembly election, Mr Sheehan will be joined by sitting West Belfast MLAs Jennifer McCann, Paul Maskey, Sue Ramsey and Fra McCann.