LONDON — At least he wasn’t left waiting by the phone.
British officials expressed relief that Prime Minister Boris Johnson was included in President-elect Joseph R. Biden Jr.’s first round of calls with foreign leaders on Tuesday, along with Chancellor Angela Merkel of Germany, President Emmanuel Macron of France and Prime Minister Micheal Martin of Ireland.
Some worried that Mr. Johnson’s ideological kinship with President Trump and his backing of Brexit, which Mr. Biden had opposed, would put him at the back of the queue, as President Barack Obama once warned Britain if it voted to leave the European Union.
But the inclusion of pint-size Ireland on the list was at least as telling as Britain’s, a red flag to diplomats that Brexit could still get in the way of the country’s cherished special relationship with United States.
Mr. Biden spoke to Mr. Martin right after Mr. Johnson, according to Irish officials. He delivered the same message to both men — that he “reaffirmed his support for the Good Friday Agreement in Northern Ireland,” according to a statement issued by the Biden transition office.
Downing Street made no mention of Northern Ireland in its account of the call, preferring to focus on how Mr. Johnson and Mr. Biden pledged to cooperate on “shared priorities, from tackling climate change, to promoting democracy and building back better from the coronavirus pandemic.”
The Good Friday Agreement, brokered in 1998 under President Bill Clinton, ended decades of sectarian violence in Northern Ireland. It has become a potential source of conflict between Mr. Biden and Mr. Johnson because Britain’s trade negotiations with the European Union could put the accord in jeopardy.
“It’s really quite pointed and deliberate that Biden raised the Good Friday Agreement with Johnson,” said Bobby McDonagh, a former Irish ambassador to Britain. “The British do not like it in general when American presidents raise Ireland with them, going back to Thatcher and Reagan.”
Mr. Biden, who speaks often of his Irish roots, warned Mr. Johnson during the campaign not to take any steps that would undermine the accord. That came after the Johnson government introduced legislation to rewrite parts of its Withdrawal Agreement with the European Union that address Northern Ireland. The revisions, critics say, could lead to the resurrection of a hard border across Ireland.
Downing Street contends that the legislation, known as the Internal Market Bill, is meant to ensure that trade flows freely between Britain and Northern Ireland and is merely a safety net in case there is no trade deal. If Mr. Johnson does strike one, he could always remove the offending language.
By all accounts, Mr. Biden and Mr. Johnson did not get into the weeds in their 20-minute exchange. The two have never met, and the prime minister carries some baggage. He alienated people in Mr. Obama’s circle by once referring to “the part-Kenyan president’s ancestral dislike of the British Empire.”
This time, Mr. Johnson seemed determined to get off on the right foot. He invited Mr. Biden to attend a climate change conference in Glasgow next November and hailed Vice President-elect Kamala Harris for her “historic achievement.” And it was noteworthy that he invoked the slogan “building back better,” one used by both the Biden campaign and his government.
The Irish were evidently less nervous about a call to Mr. Martin. His office tweeted that he had a “very positive” conversation with Mr. Biden, then abruptly deleted it — he had not yet spoken to the president-elect.
For many in Britain, it was enough that Mr. Johnson remained near the top of the incoming U.S. president’s call sheet. British newspapers crowed that Mr. Biden spoke to Mr. Johnson before Ms. Merkel or Mr. Macron, though Biden officials declined to clarify the order of the calls.
Either way, it was a better showing than four years ago, when British diplomats were chagrined to learn that President-elect Donald Trump had taken calls from President Recep Tayyip Erdogan of Turkey and President Abdel Fattah el-Sisi of Egypt before one from Prime Minister Theresa May.
Even Australia’s prime minister, Malcolm Turnbull, got through, thanks to a private number for Mr. Trump that he got from the golfer Greg Norman. (That turned out to be a mixed blessing: In another call a month later, the new president heatedly rejected an Obama-era deal to take refugees from Australia, and eventually hung up on the prime minister.)
Kim Darroch, the former British ambassador to the United States, finally connected his boss to Mr. Trump by tracking down the president-elect through his secretary at Trump Tower. It was an off-the-wall experience that has little in common with Mr. Biden’s meticulously choreographed outreach to foreign leaders.
“It was a helpful signal for the British that Johnson was in the batch of the first four Europeans, and, I assume, quite a big relief for Downing Street,” Mr. Darroch said. “As expected, the Biden team are a whole lot more organized about this than Trump. You didn’t find Erdogan and Sisi getting the first two calls.”