Carrie Symonds is now married to the prime minister – but her influence inside Number 10 has already been under scrutiny.
The couple announced their engagement in February 2020, at the same time they confirmed they were expecting a baby in early summer.
But events took a worrying turn in April that year when Mr Johnson fell seriously ill with coronavirus and spent three nights in intensive care – the same month Ms Symonds gave birth to their son Wilfred.
Mrs Johnson later said that life got “very dark” at times while her then husband-to-be was in hospital.
The pair were the first unmarried couple to live in Downing Street, having moved in together in July 2019 after Mr Johnson replaced Theresa May as prime minister.
But since then, concerns have been raised about Mrs Johnson’s influence and surrounding the couple’s finances.
In February, Downing Street was forced to deny claims that Mr Johnson’s partner had taken a central role in running the country.
It came after think tank The Bow Group, which counts Tory MPs and peers among its members, called for an independent inquiry into her “position and authority”.
This followed the appointment of two of her allies, Baroness Finn and Henry Newman, as key advisers in Number 10.
Mrs Johnson has also clashed with the prime minister’s former top aide Dominic Cummings, who alleged that she had distracted Mr Johnson from the pandemic by “going crackers” over “trivial” stories in the press about the couple’s dog Dilyn.
Mr Cummings accused her of trying to change appointments and get her friends jobs, saying this “was not only completely unethical but was also clearly illegal”, and confirmed his resignation was “definitely connected” to this.
In recent weeks, Mr Johnson has faced intense pressure to explain how he paid for the refurbishment of his Downing Street flat, which was overseen by Mrs Johnson and was reported to have cost £200,000.
The PM was later found not to have broken the ministerial code over the renovation, which Tory life peer Lord Brownlow paid towards.
Meanwhile, Number 10 refused to deny reports earlier this month that Conservative donors were approached to pay childcare costs for Boris Johnson’s son.
Mrs Johnson, who is 23 years younger than her husband, describes herself on her Twitter profile as a “conservationist… fighting plastic pollution”.
In January, the 33-year-old was appointed head of communications for animal conservation group the Aspinall Foundation.
It later emerged the foundation is under investigation for “serious concerns” over its “governance and financial management” by the Charity Commission.
Long before her relationship with the PM, Mrs Johnson had been in the so-called Westminster Bubble.
The daughter of Matthew Symonds, a co-founder of The Independent newspaper, she became the Tory Party’s head of PR aged just 29.
Prior to the role, Mrs Johnson was a special adviser to Sajid Javid during his tenure as communities secretary after a similar stint as John Whittingdale’s “spad” (special adviser) during his time at the top of the Department of Culture, Media and Sport.
She also worked on Zac Goldsmith’s failed bid to succeed Mr Johnson as London mayor.
Mrs Johnson joined the Tory party media machine in 2009, first as a press adviser, then head of broadcast at Conservative Campaign Headquarters ahead of the 2015 general election.
Her association with her husband dates back several years, having worked on his successful re-election bid as London mayor in 2012.
Prior to political PR, Mrs Johnson had several jobs in the world of commercial communications and marketing.
She graduated from the University of Warwick with a bachelors degree in theatre studies and history of art in 2009.