The spacecraft, brainchild of British entrepreneur Richard Branson, took off nestled under the wing of its mothership White Knight Two (WK2).
In the future, WK2 will carry SpaceshipTwo to around 50,000 feet (16 kilometers) before dropping the smaller spaceship and allowing it to fire up its rocket motor to launch into space.
Monday's test flight, which lasted just a few minutes, was the first in which both aircraft went aloft without separating. The test flight was carried out about 130 kilometers (80 miles) northeast of Los Angeles.
Branson announced the flight in a brief statement on his Twitter micro-blogging site.
Virgin Galactic aims to become the world's first commercial company to promote space tourism.