There was some speculation as to whether Symonds, who has quickly become an integral part of British tabloids, would join Johnson at the residence. The PM's office told CNN last week that it did not know if the couple would live together.
The move will make Johnson the first ever Prime Minister to live in Number 10 with an unmarried partner.
Johnson won the Conservative Party leadership election last week and was named prime minister on Wednesday. Symonds joined his adjutant at the door of Number 10 as he delivered his first speech as leader. Wait until you meet his girlfriend. "src-mini =" // cdn.cnn.com/cnnnext/dam/assets/190725090013-02-carrie-symonds-0724-small-169.jpg "src-xsmall =" // cdn.cnn.com/cnnnext /dam/assets/190725090013-02-carrie-symonds-0724-medium-plus-169.jpg "src-small =" http://cdn.cnn.com/cnnnext/dam/assets/190725090013-02-carrie- symonds-0724-large-169.jpg "src-medium =" // cdn.cnn.com/cnnnext/dam/assets/190725090013-02-carrie-symonds-0724-exlarge-169.jpg "src-large =" //cdn.cnn.com/cnnnext/dam/assets/190725090013-02-carrie-symonds-0724-super-169.jpg "src-full16x9 =" // cdn.cnn.com/cnnnext/dam/assets/190725090013 -02-carrie-symonds-0724-full-169.jpg "src-mini1x1 =" // cdn.cnn.com/cnnnext/dam/assets/190725090013-02-carrie-symonds-0724-small-11.jpg " data-demand-load = "not-loaded" data-eq-pts = "mini: 0, xsmall: 221, small: 308, medium: 461, large: 781" />
She has also had a successful political career and was part of the election campaign eams, which helped Johnson be re-elected mayor of London in 2012.
Symonds Becomes the Youngest – Each party communications director who is 29 years old and analysts say she has been instrumental in cleaning up Johnson's famously neglected personality during the leadership campaign.