The Secretary of State has insisted Northern Ireland's voice will still be heard at a key Government Brexit committee despite his omission from its core membership.
James Brokenshire said he is "entirely satisfied" with the arrangement that will see him invited to attend the European Exit and Trade Committee only when permanent members think his presence is required.
The Welsh and Scottish secretaries will also attend on that basis, which has prompted claims from political rivals that the devolved regions are not central to the Government's Brexit planning.
Prime Minister Theresa May will chair the Brexit committee. Its 12 core members include Foreign Secretary Boris Johnson, Brexit Secretary David Davis and Chancellor, Philip Hammond.
"I am able to attend meetings of that committee where there are Northern Ireland-related issues," said Mr Brokenshire.
"I am confident I am able to represent Northern Ireland's view, Northern Ireland's perspective, into the Brexit consideration and absolutely remain at the heart of discussions across Whitehall in ensuring the voice of Northern Ireland is heard loud and clear, and I am that champion to ensure that the issues that matter to Northern Ireland are properly reflected into the negotiation," he stated.
In an interview with BBC Radio Ulster, he added: "I am entirely satisfied that the arrangements that are in place are appropriate for me to advocate very firmly the views of Northern Ireland, and to ensure we do have that loud voice in Whitehall underlining the key themes."
SDLP leader Colum Eastwood MLA described Mrs May's decision to relegate the Secretary of State to a part-time member of the 'Brexit cabinet' as a slap in the face to the people of Northern Ireland and Scotland who voted to remain in the EU.
"Not only will the First and deputy First Ministers be shut out of negotiations, the British Government's most senior representative for Northern Ireland has been relegated to a part-time member of Theresa May's band of Brexiteers," he said. "That's a slap in the face to the people of Northern Ireland, and Scotland, who voted to remain."
Mr Eastwood added: "It also reveals that the British Prime Minister believes that there is a hierarchy of voters, and in her hierarchy people in Northern Ireland and Scotland come dead last.
"In case she needs reminding - the people of Northern Ireland and Scotland voted to remain in the European Union. Our will cannot be overridden by people in England, Wales or anywhere else.
"Either we remain in the EU or we retain the benefits of EU membership through legally recognised special status. That means retaining the free movement of people, goods and services across the island, access to the single market, maintaining our basic human rights framework and resourcing local projects with European funding streams."