The recording artist - who hit the charts in 1978 with I Lost My
Heart To A Starship Trooper - said she was "realising her dream" with the trip.
The classical singer will be the first space tourist since a hiatus in the programme in 2009 and will travel in a three-person crew to the ISS.
Brightman, who has starred in West End musicals including The Phantom of the Opera, will find out her flight schedule shortly and will embark on six months of training in Russia before the trip.
Flights are expected to continue next year.
She told a news conference in Moscow: "This voyage is a product of a dream, my dream. Finally it can be a reality. I am more excited about this than anything I have done in my life to date".
Other space tourists have included Cirque du Soleil founder Guy Laliberte and British entrepreneur and video game developer Richard Garriott.
