In spite of speculation earlier in the year surrounding her position as leader, Harney's announcement surprised many.
According to the party's constitution, if there is just one candidate for the leadership of the Progressive Democrats, this person will be elected leader by acclamation.
If several candidates put their names forward, an electoral college will determine the next leader.
Councillors, national executive members and trustees of the party will form the second group which represent 30% of the votes.
The third group contains party members for more than one year prior to the date of the leadership election.