Mr Heaton-Harris was unveiled as Ms Truss’ first Cabinet Secretary for a devolved nation on social media late last night. The 54-year-old will replace Shailesh Vara who took on the role for just 62 days during Boris Johnson’s final days in Downing Street. The Brexit-backing MP for Daventry served as Chairman of the European Research Group between 2010 and 2016 and previously described himself as a “fierce Eurosceptic”.
Mr Heaton-Harris, who is also a qualified football referee, has previously held ministerial positions in the Transport Department and Foreign Office.
He also served as Boris Johnson’s Chief Whip and as Brexit Minister under Theresa May.
Responding to his promotion on social media, Mr Heaton-Harris said: “Honoured to be appointed Secretary of State for Northern Ireland.
“Looking forward to questions in the House tomorrow morning, heading out to NI and getting to work with the Northern Ireland Office.”
Democratic Unionist Party leader and Lagan Valley MP Sir Jeffrey Donaldson congratulated Mr Heaton-Harris on his appointment.
Sir Jeffrey, himself a Brexiteer and opponent of the Northern Ireland Protocol, said on Twitter: “Congratulations Chris Heaton-Harris on your appointment.
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“[I] look forward to working with you to build a more stable and prosperous future for everyone in Northern Ireland and making the Union work for all our citizens.”
Speaking to BBC News NI, he added: “He was formerly a minister involved in negotiations with the EU about resolving the issues on the Protocol and getting Northern Ireland’s place in the internal market restored.
“Recently he’s been chief whip, I’ve worked closely with him on the Protocol bill, so he understands the issues that are confronting us at this time and I’m hopeful that as secretary of state he will bring that voice to the cabinet table to get this done, get a solution on the Protocol and then let’s move on.”
Fellow Brexiteer and Traditional Unionist Voice leader Jim Allister said Mr Heaton-Harris had been on the “same side in Eurosceptic battles in Brussels”.
He added: “I always found him good to work with. I trust he will play an active part in delivering NI from the iniquitous Protocol.”
However, Social Democratic and Labour leader Colum Eastwood appeared somewhat less receptive to Mr Heaton-Harris.
Mr Eastwood, who is anti-Brexit and supports negotiations with the EU on maintaining the Protocol, said: “Chris’ politics are totally different to mine, he’s a very hardline Brexiteer, but I know him, I like him, he seems to be a good enough guy.
“But what we really need now are some grown-ups in the British Government, prepared to properly sit down and negotiate with the European Commission, that’s the only way any of these issues will be resolved.”
Irish Foreign Minister Simon Coveney also called on Mr Heaton-Harris to help return a “functioning executive” to Northern Ireland.
He said: “Congratulations to Chris Heaton-Harris for his appointment as new Sec of State for Northern Ireland.
“I’ve known him since we were both members of the European Parliament and I look forward to working closely with him in the coming months.
“First job – a functioning executive for Northern Ireland.”
Following Stormont’s devolved elections in May, DUP MLAs refused to assent to the election of a Speaker after Sinn Fein became Northern Ireland’s first nationalist party to win an election.
The decision taken by Mr Donaldson and his colleagues, which was inspired by their opposition to the Northern Ireland Protocol, meant Ulster’s Assembly could not continue with other business, including the appointment of an executive.
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However, officials in Brussels have also put pressure on Ms Truss to respect the Northern Ireland Protocol.
European Commission President Ursula von der Leyen even said Britain must “respect” its commitments under the Northern Ireland Protocol if it wants a “constructive relationship” with the EU.
Irish Taoiseach Micheal Martin added a “pathway” to resolving the matter can be found “if there is a will” and claimed Dublin will work with London and Brussels “to do the practical and sensible thing”.
Ms Truss, who became a convert to the Brexit cause having initially campaigned for the UK to stay in the European Union, claimed the Protocol was “undermining” the Good Friday Agreement.
Writing in July, the ex-Foreign Secretary said: “Ideally, we would fix these problems through negotiation, but the EU has ruled out changing the text of the protocol.
“Northern Ireland has been without a fully functioning executive since February because of the protocol, at the time of a cost of living crisis and many other challenges.
“Therefore it is the duty of this government, as co-signatory and co-guarantor of the agreement, but also as the sovereign government in Northern Ireland, to act.”