The wedding took place in a “small ceremony” on Saturday afternoon, a Downing Street spokesman said.
The spokesman added that the couple would celebrate again with family and friends next summer, with their honeymoon also delayed until then.
The prime minister has already returned to work.
He is the first PM to get married while in office in nearly 200 years.
The Mail on Sunday reported that 30 guests were invited to the ceremony at short notice – the maximum number of attendees allowed under Covid restrictions in England.
A small number of church officials were involved in preparations for the Catholic ceremony, which was officiated by Father Daniel Humphreys, it said.
Although Mr Johnson, 56, has been married twice before, the Roman Catholic Church can allow divorcees to remarry if the previous marriages were outside the Roman Catholic Church.
Christopher Lamb, religious correspondent for Catholic magazine The Tablet, told BBC Radio 5 Live: “There will be a feeling that, why are some people who are divorced allowed to be married in the church and others not?
“And I think that’s where the church I think can look at its current roles and see how it can become more welcoming. It has been welcoming to Boris Johnson, why not to others?”
In the same segment, Father Mark Drew, assistant priest at St Joseph’s Church in Penketh, Warrington, said he has previously told Catholic couples going through an annulment or divorce that they are not able to remarry in the Church.
“It looks to them – rightly or wrongly – as if the Church is applying double standards and I do fear that this decision does make the Church look bad.”
Just one official photograph has been released – the day after the wedding – showing the couple in the garden at 10 Downing Street in the hours following the ceremony.
However, Conservative MP James Cleverly shared a different photograph of the newlyweds enjoying their garden reception in the Saturday sunshine, with decorations and a table of refreshments visible in the background.
— James Cleverly (@JamesCleverly) May 30, 2021
Downing Street did not reveal any details of who was invited and whether any of Mr Johnson’s Cabinet colleagues were among the guests.
Several politicians have congratulated the couple, including Home Secretary Priti Patel, Vaccines Minister Nadhim Zahawi and Work and Pensions Secretary Therese Coffey.
Ms Patel wrote on Twitter: “Many Congratulations to Mr & Mrs Johnson @BorisJohnson and @CarrieSymonds. Wishing you both much love and happiness.”
Musicians were pictured leaving No 10 on Saturday night.
Members of the public were asked to leave Westminster Cathedral just after 13:30 BST, the Sun reported.
The new Mrs Johnson – who has confirmed she will take her husband’s surname – wore a white dress to exchange vows with the prime minister.
The last prime minister to get married while in office was Robert Banks Jenkinson in 1822.
Mrs Johnson used to work in the Conservative Party press office, which she joined in 2010, and two years later she worked on Mr Johnson’s successful campaign to be re-elected as mayor in London.
She became the party’s head of communications before leaving in 2018 to work in public relations for marine conservation organisation Oceana.
The couple were first romantically linked by the media in early 2019. In February 2020, they revealed that they were engaged and that she was pregnant.
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