Mr Johnson, the former Mayor of London, will become the 14th premier of the Queen’s reign when the handover of power takes place at Buckingham Palace.
He vowed to delver Brexit by October 31, unite the country and defeat Labour leader Jeremy Corbyn after winning the endorsement of Tory activists.
The 55-year-old secured 92,153 votes – nearly double the number accrued by Jeremy Hunt, his successor as Foreign Secretary, during a protracted campaign.
Yet, while Mr Johnson spent last night finalising his first Cabinet and accepting congratulatory messages from President Donald Trump and other world leaders, Mrs May set out her own hopes as she prepares to leave 10 Downing Street for the final time.
In a letter to The Yorkshire Post, she praised this newspaper’s role in the Power Up The North campaign – a joint collaboration between 33 publications which was launched at the outset of the Tory leadership contest.
Crediting this newspaper with being “at the forefront of making the case for the North”, she cited new investment for transport and the enhanced role recently given to Jake Berry, the current Northern Powerhouse Minister, as evidence of her commitment to this region.
And referencing the commitments made by both Mr Johnson, and his rival, during the campaign, she said one of the new PM’s “top priorities” must be “to do all they can to unlock the North’s vast potential”.
“There is much more to do, which is why investing in and supporting the North must remain a top priority for the Government.”
Her sentiments were echoed by CBI regional director Beckie Hart who appealed to Mr Johnson: “Let’s work together to get our economy back on track and working for communities everywhere. My message is clear - Boris, it is time to back the Northern Powerhouse.”
Meanwhile Henri Murison, director of the Northern Powerhouse Partnership, said Mr Johnson now “has key choices to make around education and skills, around devolving powers and funding as well as of course to focus on transport where he has rightly committed to Northern Powerhouse Rail.
He added: “Closing the economic divides between North and South is vital to ensure we can make this a fairer country, raise productivity and meet the challenge of the global race.”
Mr Johnson signalled at the leadership hustings in York that he intended to give a Cabinet minister specific responsibility for the North, though his plans have been overshadowed by the resignations of a raft of ministers who don’t support his advocacy of a no-deal Brexit.
Meanwhile Mrs May also uses her farewell letter to praise the “incredibly valuable progress” that this newspaper, and many others, have achieved on the issue of loneliness – an issue inspired by the late Batley & Spen MP Jo Cox.
Confident that the award-winning campaign “will continue to bear fruit for years to come”, the outgoing PM’s support support comes as Kim Leadbeater, the murdered MP’s sister, appeals to Mr Johnson – and all political leaders – to tone down their political rhetoric and “listen to people’s genuine concerns”.
Urging Mr Johnson to “conduct himself in an appropriate way for someone in a position of such importance”, she writes in today’s newspaper as part of a special series on what the next PM can do for Yorkshire.
“For me, language matters. The toxicity of public discourse has reached a new low in the last three years and politicians of all persuasions have a responsibility to do something about it.”