Froome will make his first appearance in the British race since 2009 instead of defending his Vuelta title, while Thomas returns to the race on home shores after winning his maiden Tour title last month.
The pair will be joined by Dutchman Wout Poels when the race begins at Pembrey Country Park, Carmarthenshire, on September 2.
Tour of Britain
Alaphilippe wins Tour of Britain
09/09/2018 AT 16:36
"As soon as I'd finished the Tour I knew I wanted to ride the Tour of Britain and race on home roads," Thomas said in a statement.
"I want to go to the race in the shape to compete and enjoy it," Thomas added. "We'll have to see how the next few weeks go but I'm looking forward to it and I know we will have a strong team there. Wout is looking really good at the moment too."
Six-time Grand Tour winner Froome will be racing his first Tour of Britain as a Team Sky rider, while Thomas finished seventh overall last year.
Their participation rules them out of the Vuelta a Espana, which starts on August 25.
"The Vuelta a Espana has always been such a big goal and sadly coincided with the Tour of Britain, but not doing La Vuelta this year gives me the chance to come back to the UK and race on what looks like a great parcours," Froome said.
Froome returned an Adverse Analytical Finding for Salbutamol following a urine sample at last September's Vuelta, but the International Cycling Union cleared him of wrongdoing ahead of last month's Tour de France, where he finished third.
Tour of Britain
Stannard soloes to victory in gloomy Mansfield
08/09/2018 AT 15:40