James Brokenshire, an ally of new British prime minister Theresa May, is to replace Theresa Villiers as Northern Ireland Secretary.
Mr Brokenshire, a former Home Office minister, campaigned for a Remain vote in the recent EU referendum and said it was a great honour to take on the job.
He said he looked forward to “working closely over the coming weeks and months with the Northern Ireland Executive, the Irish Government and the whole community in Northern Ireland to build a brighter, more secure future for everyone”.
“A key priority for me is to continue with the full implementation of the Stormont House and Fresh Start Agreements, to help tackle paramilitarism, put the Executive’s finances on a secure footing and address the legacy of the past. I also want to maintain the Government’s full support for the Belfast Agreement.”
Mr Brokenshire said "another huge challenge" was ensuring that we make a success of the UK's decision to leave the European Union.
“It is vital that Northern Ireland’s interests are fully protected and advanced including in relation to the border.”
Ms Villiers said she had declined to accept the offer of another cabinet role from Ms May, who has been appointing her cabinet after taking over from David Cameron on Wednesday.
First cabinet position
Mr Brokenshire was previously in charge of security and immigration at the Home Office, having been first elected to the House of Commons in 2005. He currently represents the constituency of Old Bexley and Sidcup outside London. The Northern role is his first cabinet position.
After the Brexit referendum campaign, Mr Brokenshire attracted criticism for refusing to offer a guarantee that EU nationals would be permitted to remain in the UK during a Commons debate.
“The prime minister has been clear that decisions on issues relating to the UK’s exit from the EU will be for a new prime minister,” he said. “I’m therefore not in a position to make new policy announcement this afternoon.”
It would be a matter for reciprocal arrangements with EU countries, he said.
“This would be unwise without a parallel assurance from European governments regarding British nationals living in their countries,” he said. “Such a step might also have the unintended consequence of prompting EU immigration to the UK.”
Minister for Foreign Affairs Charlie Flanagan said he hoped to meet the new Northern Secretary soon.
“I warmly congratulate James Brokenshire on his appointment as Secretary of State for Northern Ireland and hope to have the opportunity of an early meeting with him,” he said. “The post carries significant responsibilities on important matters that remain within the competence of Westminster, such as security, parades and dealing with the legacy of the past.”
Mr Flanagan said the (Belfast) Good Friday Agreement remains the foundation stone for relations on the island of Ireland.
“I look forward to working closely with Mr Brokenshire in discharging these responsibilities in the interests of all of the people of Northern Ireland. That work assumes even greater importance in the context of the challenges arising from the decision that the UK should exit from the European Union.”
Ms Villiers said she was “sad to bring to end my work in Northern Ireland but I believe that I leave the political situation there in a more stable position than it has been for many years.
Her exit was met by contrasting reactions from Stormont’s two main parties - the DUP and Sinn Féin.
DUP leader Arlene Foster tweeted: “I enjoyed working with her & wish her all the best for the future.”
Sinn Féin MEP Martina Anderson said “Theresa Villiers will be no loss - all British secretary of states should stay over there”.
In Ms May’s cabinet shake-up, Patrick McLoughlin has been moved from the department for transport to become chairman of the Conservative Party and chancellor of the Duchy of Lancaster, replacing Oliver Letwin. Chris Grayling will take over as transport secretary.
Jeremy Hunt is to remain as health secretary and failed Conservative Party leadership candidate Michael Gove saw his justice secretary job go to Liz Truss, who became the first female lord chancellor in the 1,000-year history of the role.
Nicky Morgan, who had been education secretary, and John Whittingdale, the culture secretary, have also lost their jobs. Ms Morgan supported Mr Gove's leadership bid.
Ms Morgan’s former role as education secretary went to another promoted woman, Justine Greening.
Mr Whittingdale, whose tenure as culture secretary had seen a major re-examination of the BBC, tweeted that he had “left the job”.
Andrea Leadsom, who also stood against Theresa May in the Conservative Party leadership contest, has been appointed environment secretary.
Meanwhile, Stephen Crabb resigned from his role as work and pensions secretary, “in the best interests of my family”, days after The London Times reported that he had sent sexually explicit WhatsApp messages to a young woman during the EU referendum campaign.
Ms May's first appointment was Philip Hammond as chancellor of the exchequer, replacing Mr Cameron's close ally George Osborne. Mr Hammond's old post as foreign secretary went to Boris Johnson.
The former London mayor had been tipped to succeed Mr Cameron after the EU referendum but his stock fell drastically after he left the leadership race when challenged by his former ally Mr Gove.
Amber Rudd will take Ms May's former job as home secretary.
Brexit supporters David Davis and Liam Fox were brought back from the cold to take the roles of secretary of state for exiting the EU and minister for international trade respectively.