PM Boris Johnson replaced Michael Gove as EU relations minister with Lord David Frost, chief negotiator of last year’s Brexit deal, on Wednesday.
Downing Street said Frost would have a seat in cabinet and take over all responsibility for dealings with Brussels.
The newly-appointed EU relations ministers wants to take a more “hardline” stance on the Northern Ireland protocol, an ally of the minister has said.
Frost will also take over Gove’s job as UK chairman of the withdrawal agreement joint committee and the partnership committee to oversea the implementation of the Brexit trade deal.
Frost will be in charge of talks on easing trade restrictions between Great Britain and Northern Ireland.
Gove is expected to step up his work strengthening ties between countries of the United Kingdom as head of the Cabinet Office “union unit” in the run-up to elections in May.
Johnson has also asked Gove to chair the national recovery taskforce subcommittee dealing with public services, including the backlog in the courts, the NHS, schools and universities.
Frost was originally offered the post of national security adviser, a move which was criticized by some MPs including former PM Theresa May due to his perceived lack of experience, but the offer was withdrawn and given to Sir Stephen Lovegrove at the end of January.