Sinn Féin’s John O’Dowd is to challenge Michelle O’Neill’s position as vice president of the party.
In a tweet on Saturday, he confirmed he would be seeking nominations ahead of the party’s annual election for leadership roles.
This will take place in November at the party’s ard fheis (annual conference).
Mrs O’Neill confirmed she would be seeking re-election and said she welcomed “democratic debate and choice”.
She added that the party is “fully focused on the threat of Brexit” and she is “fully committed to this work”.
Mr O’Dowd’s candidacy was revealed in the Belfast Telegraph on Saturday.
Mr O’Dowd is a former Stormont education minister and the party’s Upper Bann MLA.
Mrs O’Neill was given her first leadership position by the party in 2017 when she took over from Martin McGuinness who stepped down due to illness.
She was announced as Sinn Féin’s new “leader in the north” on 23 January that year, two months before the death of Mr McGuinness.
Mrs McDonald was elected as party president, replacing Gerry Adams who stepped down after 35 years.
Mr O’Dowd briefly filled in as deputy first minister in 2011, when Mr McGuinness ran as a candidate in the Irish presidential elections.
If he wins the nomination he would take the position of deputy first minister in a future Stormont executive.
Mr O’Dowd tweeted: “I can confirm I will be seeking nominations for leas uachtarán (vice president) of Sinn Féin as we approach the Ard Fheis and the annual election of party leadership.
“I look forward to the debate across the party and island.”