He joins from the Samling hotel in Cumbria, where he has held a Michelin-star for the last three years.
It comes weeks after Gillan announced he would be leaving the Exclusive Hotels-owned South Lodge at the end of April after a ten-year stint.
Swainson said: “I am really looking forward to developing my food within such an established restaurant and cannot wait to get started.”
David Connell, general manager at South Lodge, said the hotel was looking forward to the chef bringing his ‘vision and creativity’ to the restaurant.
“Working within a few feet of our guests, Ian has a unique opportunity to showcase his culinary talent and engaging personality and offer diners a truly interactive and memorable dining experience,” said Connell.
Swainson has been cooking for over 15 years in kitchens including the Michelin-starred L'Ortolan in Reading, Seaham Hall in County Durham, Le Becasse in Ludlow and Chewton Glen in Hampshire.
The Samling was crowned the Best Dining Boutique Hotel in the World under his watch at the 2012 Boutique Hotel Awards.
He joins a host of award-winning chefs working across the Exclusive Hotels portfolio, including Matt Worswick at Pennyhill Park and Olly Rouse at Lainston House.
The group runs six hotels and two golf clubs across the UK.