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.
Long before her relationship with the PM, Mrs Johnson was already in the so-called Westminster Bubble as she achieved a meteoric rise in political PR.
She became the Conservative Party's director of communications at the age of just 29, the youngest-ever person to take on the role.
She was also listed in the top 10 figures in political communications by trade magazine PR Week in 2018 - second only to then-Number 10 chief Robbie Gibb.
Mrs Johnson - who at 33 is 23 years younger than her husband - was credited with helping improve Mr Johnson's image as he sought to become prime minister in 2019.
It was reported that he started sporting a smarter hair cut, lost weight and began to rein himself in from impromptu and off-hand soundbites for the media.
Before Mr Johnson won the Tory leadership contest, the couple hit the headlines in June 2019 after police were called to their south London home as neighbours had reportedly heard a loud argument.
The following month, the pair became the first unmarried couple to live in Downing Street when Mr Johnson replaced Theresa May as prime minister.
But since then, concerns have been raised about Mrs Johnson's influence inside Number 10 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 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 the Johnsons' son Wilfred.
In January, Mrs Johnson 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.
She has previously successfully campaigned to reverse the decision to release black cab rapist John Worboys from prison, after revealing she was given a lift by him when she was 19.
During her early career, 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.
The daughter of Matthew Symonds, a co-founder of The Independent, and newspaper lawyer Josephine Mcaffee, Mrs Johnson describes herself on her Twitter profile as a "conservationist" and someone who is "fighting plastic pollution".
She is also a fan of the BBC comedy series Fleabag, once tweeting that creator and star Phoebe Waller-Bridge was a "total genius".
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.