Arriving Monday at the Prime Minister's residence, the 15-week-old puppy was carried in a red travel container, flanked by an entourage of humans.
The puppy -- believed to be a Jack Russell crossbreed -- was rescued by Friends of Animals Wales, a small, volunteer-run charity based in South Wales.
According to Friends of Animals Wales, which specializes in taking in and re-homing animals, the dog "started his life in a Welsh puppy farm."
It's uncertain how Larry the cat -- 10 Downing Street's well-established feline resident -- will take the news.
"We knew that Carrie Symonds has always been a huge animal welfare advocate and we are absolutely overjoyed that this gorgeous pup will be living his best life with Carrie and the Prime Minister at their Downing Street home," Friends of Animals Wales said in a press release.
"To think our little 'wonky' pup started his life in a Welsh puppy farm and was destined for an uncertain existence at the hands of a puppy dealer, but is now going to be with people who absolutely adore him is a dream come true," the charity said.
In the statement released online, Friends of Animals Wales was keen to raise awareness of Lucy's Law -- a new law aiming to crack down on "puppy farms" in England, which is due to come into effect next year.
"We know only too well why Lucy's Law is such an important piece of legislation," the charity said, "because we pick up the pieces of third-party puppy selling every day."