'Today, for the first time in history, a crewed spaceship, built to carry private passengers, reached space,' Branson, company's head said in a statement afterwards.
Virgin Galactic's SpaceShipTwo, VSS Unity, flew higher than it ever has before on Thursday, surpassing what the US Air Force considers the boundary of space, and marking the first manned flight to space from US soil since 2011.
No spacecraft with people on board has taken off from US soil since the American space shuttle program ended, as scheduled, seven years ago.
Since then, the world's space agencies have relied on Russian Soyuz rockets to ferry astronauts to the International Space Station.
The brief, suborbital flight with two pilots on board was a key milestone for the company headed by British tycoon Richard Branson, who is striving to send tourists to space at a cost of $250,000 per seat.
More than 600 clients have already paid $250,000 for a ticket.
Branson told CNN in November he hoped to send people to space "before Christmas."
Virgin Galactic has said it would use the US Air Force's definition of space as its standard.
The US space agency paid Virgin Galactic to fly four space science and technology experiments on the VSS Unity, "making this Virgin Galactic's first revenue generating flight," the company added.
Virgin Galactic's spaceship did not launch on a rocket but took off attached to an airplane from Mojave, California.
After reaching a certain altitude, higher than 43,000 feet (13,100 meters), it fired its rocket motors for 60 seconds and made it to a peak height, or apogee, of 51.4 miles (82.7 kilometres).
Virgin's first flight date had been pushed back multiple times, following a test flight accident that killed a co-pilot in 2014.
Another US rocket company, Blue Origin, founded by Amazon CEO Jeff Bezos, is also working to send tourists to space, but using a small rocket to get there.
SpaceX and Northrop Grumman operate cargo ships that launch from the United States, toting supplies and food to the space station, but not people.
The first crew tests of SpaceX and Boeing's astronaut capsules are expected next year.