Jeffrey Donaldson has announced his bid to become the next leader of the Democratic Unionist Party (DUP).
Northern Ireland’s Agriculture Minister Edwin Poots has already declared for the DUP leadership.
The contest follows Arlene Foster decision to step down as party leader at the end of May.
It will be the first leadership contest in the DUP's 50-year history.
Mr Donaldson announced his bid on the anniversary on the creation of Northern Ireland.
It was 100 years ago on 3 May 1921, that Northern Ireland became a new legal entity by partition..
Mr Poots had received the backing of the majority of the party's MPs and MLAs who make up the electoral college.
However, Sir Jeffrey has also received significant endorsements, according to his team.
In announcing his leadreship bid today, the Lagan Valley MP first praised the work of the party's outgoing leader, saying Mrs Foster had shown "great courage and conviction and a big heart for Northern Ireland".
In order to become party leader, the winning candidate will need to secure the support of at least 18 of the party's MLAs and MPs.
Today, on this centenary day for Northern Ireland I am delighted to announce that I am putting my name forward for the leadership of the @duponline I would count it a great honour to serve my party & country in this role. #strong #united #focused pic.twitter.com/yXhfipbXPS— Jeffrey Donaldson MP (@J_Donaldson_MP) May 3, 2021