The chef – who has appeared on Saturday Kitchen and James Martin’s Brittany series – will oversee the catering at four Kew outlets.
The Orangery Restaurant, Victorian Plaza Cafe, White Peaks Café, and the outdoor Pavilion cater for an estimated 1.35m visitors a year.
Keogh brings over 20 years’ experience to the job, including stints at D&D’s The Avenue, Roast and The Wolseley – where he was head chef for four years until 2015.
“I am very much looking forward to working with Peyton and Byrne at Kew," said Keogh.
“Being such an iconic attraction, I am delighted to be building on its success, showcasing the best of British through its menus and dining experiences."
Peyton and Byrne handles the catering at some of London’s major attractions including the British Library, the Royal Academy of Arts and St James’s Park.
In 2015 the firm extended its nine year contract with the National Gallery until 2023 in a £36m deal.