KKR – which already owns retail giants such as Alliance Boots and Toys R Us – bought the Pets at Home chain from fellow buyout specialist Bridgepoint.
Pets at Home was founded in 1991 and bought by Bridgepoint for 230m in 2004.
In the year to the end of March, the pet company – which also owns 54 veterinary practices – posted underlying profits of 70m on turnover of 404.2m.
The company has been growing at the rate of about 20 new outlets a year and is likely to maintain this pace under its new ownership.
John Pfeffer, the head of European retail at KKR, said: "We are enthusiastic about the significant further potential for Pets at Home to grow, develop and continue to deliver its unmatched breadth of products, store environment, competitive pricing and customer service."
The winter chill saw a 70 per cent surge in demand for dog coats, as animal lovers looked to protect their pets from the cold, while sales of rabbit-hutch covers also rose.
Overall, like-for-like sales for the six weeks to 7 January were up 6.7 per cent year-on-year, a slight slowdown from the 9.8 per cent growth seen in the first 41 weeks.
Chief executive Matt Davies said KKR's move was a "resounding endorsement of our success to date".
KKR is believed to have seen off rival bids from Apax, Bain and TPG, as well as tempting Pets at Home away from a possible stock market flotation.