Boris Johnson has drafted former Brexit negotiator Lord David Frost into his cabinet to take charge of forging a new relationship with the EU.
He will seek to maximise post-Brexit trading opportunities when he becomes a full cabinet member next month, Downing Street said.
He will also replace Michael Gove as co-chair of a committee on implementing the Brexit withdrawal deal.
Mr Gove will keep his seat at the cabinet table.
The change means Mr Gove, who will keep the title of Chancellor of the Duchy of Lancaster, will be Lord Frost's new boss at the Cabinet Office.
The peer said Mr Gove had done an "extraordinary job for this country" in talks with the EU over the past year.
In taking over from him as chair of the EU-UK committee tasked with implementing the Brexit deal, he said: "I stand on the shoulders of giants."
Labour's shadow international trade secretary Emily Thornberry tweeted: "So we've finally got one minister taking a grip of the problems with our post-Brexit trading relationships with Europe.
"Someone who has never been elected by anyone in this country, and won't be accountable in the House of Commons to any of us who have."
This appointment again shows that Brexit didn't end with the signing of a trade deal.
While the UK is no longer a member of the EU, negotiating with Brussels and member states will preoccupy this and future governments for years to come.
Since the start of the year (and the end of the transition period) serious tensions have flared up between Westminster and Brussels over trade disruption between Great Britain and Northern Ireland and vaccine supplies.
Other issues, such as the City of London's access to EU markets, remain unresolved.
Lord Frost will now be the UK minister responsible for co-ordinating all this and it will be a full time job.
Rather than responsibility for the EU being shared between several departments - such as the Foreign Office and International Trade - the decision to put Lord Frost in the cabinet and in charge of the Withdrawal Agreement Joint Committee gives him huge clout overseeing policy.
It also takes a lot of work away from Michael Gove and means there will be a single minister responsible to parliament for EU relations - although of course he'll be answering questions in the House of Lords and not the Commons.
Speaking last week to a select committee, Lord Frost said the UK's relationship with the EU since the trade deal between the two came into force at the start of the year, had been more "problematic" and "bumpy" than he had expected.
He said he hoped we would "get over this", but added that it was going to require a "different spirit" from Brussels.
Lord Frost - who is said to be highly rated by the prime minister - had been due to become the UK's new national security adviser earlier this month, but was replaced days before he was due to start.
He will be the co-chair of the UK-EU joint committee, which was set up to resolve differences arising from the treaty which took the UK out of the EU in February 2020.
Northern Ireland tensions
Since the UK left its Brexit transition period in January, this committee has mainly focused on overcoming trade tensions in Northern Ireland.
Unlike the rest of the UK, Northern Ireland is continuing to follow EU single market rules on goods.
This provision, agreed as part of the withdrawal agreement, was designed to get rid of the need for checks at the border with the Republic of Ireland.
But it has meant checks had to be introduced on some goods travelling between Great Britain and Northern Ireland.
Since the new rules came into force, there has been tensions at ports in Northern Ireland, with disruption to some food supplies and online deliveries.
Lord Frost will also become UK chair of a separate committee being set up to oversee the post-Brexit trade deal he negotiated with Brussels last year.