The newly-single star, who split from actress Demi Moore in November, is “thrilled” to join the line for the Virgin Galactic service, which is in its “final stages” of flight tests, Branson wrote on his blog.
“I gave Ashton a quick call to congratulate and welcome him,” wrote the multi-millionaire entrepreneur, known for his trademark publicity stunts.
“He is as thrilled as we are at the prospect of being among the first to cross the final frontier (and back!) with us and to experience the magic of space for himself.”
Linking to online video, Branson added: “As you can see .. our spaceships are not only very beautiful but are built and flying in the final stages of our exhaustive test flight program.
“We are guided by safety and so will ensure that everything is just as safe as it can possibly be before we start commercial services — particularly as I will be on the first commercial flight with my kids!” he added.
34-year-old Kutcher, who with his wife was a pioneer of social media, re-tweeted Branson’s message on his own Twitter feed, but didn’t make any other comment.
Branson opened the world’s first-ever commercial spaceport in the New Mexico desert last October, having said the previous month that he hoped to launch the first flight within 12 months.
“Spaceport America” is home to the Virgin Galactic company and is expected to house up to two WhiteKnightTwos — the aircraft which launch the orbital spacecraft themselves, and five SpaceShipTwos.
A number of private companies are rushing to fill the gap left by NASA, which ended its 30-year shuttle program last year with the completion of the final Atlantis mission to the International Space Station (ISS).
Kutcher is best known for TV shows including “That 70s Show” and “Punk’d,” and last year replaced troubled actor Charlie Sheen in the popular comedy “Two and a Half Men.”
Actress Moore, 49, was rushed to hospital in January after taking an unidentified drug which left her convulsing and “burning up,” according to an emergency 911 call.