Sir Jeffrey Donaldson, a Westminster MP, is one of two candidates to announce a bid to replace Arlene Foster as DUP leader.
The longstanding Lagan Valley MP said he would promote a positive strategy and values if elected, with a focus on building a shared future for everyone in Northern Ireland.
The party’s current Westminster leader also pledged meaningful reform within the DUP and said he would set clear policy directions on key challenges for unionism, such as Brexit’s contentious Northern Ireland Protocol.
His entry in the race to succeed the deposed Foster will mean the DUP is set for its first-ever leadership contest in its 50-year history.
Stormont Agriculture Minister Edwin Poots announced his candidature last week.
Sir Jeffrey announced his leadership bid at fellow MP Gavin Robinson’s constituency office in east Belfast on Monday morning, coinciding with the date viewed by many historians as the centenary of the creation of Northern Ireland.
“I want to thank Arlene Foster for her service to our party, people and country,” he said.
“She led with great courage, conviction and a big heart for Northern Ireland. I wish Arlene and her family well for the future.
“Today, Northern Ireland enters its second century.
“I am convinced that in this new century, Northern Ireland’s best days are ahead of us.
“We want to build a shared future for Northern Ireland where everyone, regardless of their background, has a part to play in showing the world what we are truly capable of.
“Both making our full contribution, and enjoying the benefits, of being part of the United Kingdom.”
Sir Jeffrey will be seen as the moderate candidate against the more hard-line Poots, who also represents the Lagan Valley constituency, as an Assembly member.
Foster resigned last week after an internal revolt against her leadership.
The move came in the form of a letter of no confidence signed by a majority of the party’s senior elected representatives.
Poots, understood to have been one of the key figures behind the heave against her, announced his leadership bid within 24 hours of Foster’s resignation statement.
The outgoing DUP leader will step down from that role on May 28, and as Stormont first minister at the end of June.
A small electorate, comprising just the party’s MLAs and MPs, will decide the leadership contest.
Making his pitch for the job, Sir Jeffrey added: “Our next century will be built on the politics of persuasion.
“This will need positive leadership, strategy and values. Strong. United. Focused.
“This will also require party structures capable of communicating clearly and consistently to appeal to voters; capable of working with a strong and growing team built around real partnership between representatives in our local councils, the Assembly and at Westminster; and capable of overcoming those that seek to abolish Northern Ireland.
“I will develop and swiftly implement an agreed programme of meaningful reform and clear policy direction on key challenges like the protocol.
“Our task is to not only make the case for the Union but to strengthen that Union in the years ahead.
“Our previous leaders have shown that when the DUP leads, Northern Ireland moves forward.
“We are not only elected members of a political party, we are the custodians of the Union.
“Let us take our next steps forward. Forward to a new century.”
On Sunday it emerged that Poots would not take on the first minister’s job if he was elected DUP leader, instead appointing an Assembly colleague to the role as he concentrates on the leadership.
If Sir Jeffrey won the leadership and remained as an MP at Westminster, he would not be able take up the first minister’s job.
Discontent at the DUP’s Brexit strategy was a major factor in the move against Foster, with party rank-and-file laying some of the blame for the emergence of an Irish Sea border, in the form of the protocol, at her door.
Traditionalists from the party’s religious fundamentalist wing also harboured concerns over positions Foster has taken on some social issues, in particular her decision to abstain in a recent Assembly vote on a proposed ban on gay conversion therapy – a proposal the majority of her party colleagues opposed.