Prime Minister Boris Johnson has given Lord David Frost, the man who led Britain's Brexit negotiations, a job in his top team of ministers to advise on relations with the EU.
The surprise move puts one of Mr Johnson's most trusted allies, a eurosceptic former diplomat and champion of British sovereignty, in charge of managing the post-Brexit relationship with Brussels, which has had a rocky start.
Lord Frost served as chief Brexit negotiator for the initial deal, which took Britain out of the EU on January 31 2020, and for talks on the trade deal that came into force at the end of last year.
The government had indicated that he would continue to advise it on matters relating to the EU, but his appointment to Mr Johnson's Cabinet of top ministers was not expected.
As a minister rather than an adviser, Lord Frost will have greater influence and be able to direct the work of officials.
He takes on two formal roles previously held by senior minister Michael Gove, putting him in charge of attempts to improve the trading terms for Northern Ireland and giving him a top role in helping to resolve any future disputes over the deal.
"I am hugely honoured to have been appointed minister to take forward our relationship with the EU after Brexit," Lord Frost said on Twitter.
"In doing so I stand on the shoulders of giants and particularly those of Michael Gove, who did an extraordinary job for this country in talks with EU over the past year."
Lord Frost is an unelected member of the House of Lords, Parliament's upper chamber.
His appointment will take effect from March 1, Mr Johnson's Downing Street office said.
Jill Rutter, senior research fellow at the research body, UK in a Changing Europe, said the move raised questions about how the EU relationship would be managed.
"It looked as though [Gove] was the pragmatist and Frost the sovereignty hard liner," Ms Rutter said on Twitter.
Mr Gove, who earlier led the implementation of the EU exit agreement and free trade deal, welcomed Lord Frost's appointment.
He will continue in his ministerial role in charge of the Cabinet Office.
Lord Frost will take over as the UK chairman of the Withdrawal Agreement Joint Committee.
This means he takes on responsibility for negotiating with Brussels to make the complex parts of the trade deal relating to Northern Ireland work smoothly.
The EU has so far rejected British demands for more time to solve serious disruptions to free trade between Britain and Northern Ireland from the deal.