The Sun reported that the couple have sent save-the-date cards to family and friends for an event on Saturday July 30 of next year.
Though the paper said details of where they will marry remained a secret, the prime minister’s Buckinghamshire residence, Chequers, is tipped to host the wedding. Another possible venue is said to be the Port Lympne safari park in Kent, as Symonds works for the conservation charity.
Johnson, 55, and Symonds, 33, were the first unmarried couple to live in Downing Street, moving there in July 2019, and he reportedly proposed on holiday on the Caribbean Island of Mustique.
If the wedding goes on as planned, Johnson will be the second British prime minister ever to marry while in office, following Robert Jenkinson in 1822.
The couple have lately been hit by a scandal over the costly redecoration of their Downing Street flat, which is being probed over allegations that contributions by a Tory party donor were not declared fully.
Johnson has been married twice before. He had four children with his previous wife, lawyer Marina Wheeler, before they split in 2018. The couple only finalised their divorce last November. The Prime Minister also reportedly has a daughter born as the result of an affair.