Mr Shuttleworth is to fly aboard a Soyuz craft
"Nasa and its international partners have agreed in principle to the flight of Mr Shuttleworth, and we are in the process of formalising that approval," Nasa spokeswoman Kirsten Larson said. "There are some final details that need to be taken care of," she added.
Mr Shuttleworth signed a contract with the Russian space agency earlier in December to fly aboard a Soyuz taxi mission to the International Space Station (ISS) in April 2002.
Nasa's comments are in marked contrast to their attitude to Dennis Tito's paying trip to the platform in April 2001.
'Extra stress'
The agency opposed Mr Tito's trip until the last minute, finally agreeing a protocol with the other operators of the station to govern his stay there.
It also suggested that his presence on board the platform had hampered the work of professional astronauts and placed extra stress on mission controllers.
Ms Larson said on Tuesday that the ISS partner agencies had drafted a set of requirements covering physical and mental fitness, language skills, and training needs.
Mr Shuttleworth completed an extensive training programme in Russia before he signed the contract to fly and will face more training before he joins Russia's Yuri Gidzenko and Italy's Roberto Vittori aboard the Soyuz mission in April.
Like Dennis Tito, he is reported to have paid $20m (£14m) to take part in the mission.