"I gave Ashton a quick call to congratulate and welcome him," Branson wrote in an online message Monday.
"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," Branson said. "Ashton is joining a fast expanding group of true pioneers who are on their way to a life-changing experience and a place in the history books. It's great to have him on board."
MSNBC.com said the "Two and a Half Men" and "Punk'd" star paid $200,000 for his ticket on the craft, which is expected to carry as many as six passengers a flight.
The New York Daily News said no launch date has been set. Test launches are expected to begin this year, the newspaper said.