Froome, 33, is aiming to become only the fifth rider to win five Tours, while Welsh Team Sky team-mate Thomas, 32, won the race for the first time in 2018.

Colombian Egan Bernal, 21, will lead Team Sky at the Giro in May.

Froome said it was a "difficult decision" to skip the race.

"I've got some amazing memories from last year, but I think, with the Tour de France as my main objective, it's probably better that I skip the Giro d'Italia in 2019," said the 33-year-old.

"I'm getting to the point in my career now where I'm starting to think about what kind of legacy I want to leave behind and if I am able to win the Tour de France for a fifth time and join that very elite group of bike riders - only four other people have ever done that - it would just be incredible."

The Giro - the first of the year's three Grand Tours - runs from 11 May to 2 June, and the Tour from 6-28 July.

Froome won the Giro for the first time in 2018 thanks to a spectacular 80km solo breakaway on stage 19.

Froome began the 2018 Tour as the leader of Team Sky, but ended it riding in support of Thomas after his team-mate proved to be stronger.

Thomas will also compete in the Road World Championships in Yorkshire in September.

"The main goal for me will be to go back to the Tour de France for the best result I can," he said.

"Maybe if I hadn't have won the Tour in 2018 I might have looked at a Giro/Vuelta programme but, having won the Tour, I'll have the number one on my back and it would be sad not to go back and not to go back at 100% as well."

The Vuelta a Espana, the final Grand Tour of the season, takes place from 24 August to 15 September.

In his first season at World Tour level, Bernal won the Tour of California in May and rode as a domestique for Froome and Thomas at the Tour de France.

"The Giro is a race that I really, really like," Bernal said.

"I lived in Italy for three years, so I have a lot of friends there and I really like the Italian fans. I know the roads, I really like the Giro, and I want to do a good race there."

Britain's Simon Yates, who led for 13 stages of the 2018 Giro before losing the lead to Froome, said in December that he wants to "finish the job off" in 2019.