The journey will be live broadcast with Sir Richard, two pilots and three other passengers, experiencing several minutes of weightlessness.
Sir Richard says he wants to try the experience before opening the service up to paying customers next year.
Speaking to the BBC the entrepreneur said: “I’ve wanted to go to space since I was a kid, and I want to enable hopefully hundreds of thousands of other people over the next 100 years to be able to go to space.
“And why shouldn’t they go to space? Space is extraordinary; the Universe is magnificent. I want people to be able to look back at our beautiful Earth and come home and work very hard to try to do magic to it to look after it.”
Sir Richard has lined up some 600 Virgin Galactic customers who have already paid deposits for tickets costing up to £180,000.
Today’s launch is a pivotal moment in the increasingly frantic space race between Sir Richard and two other billionaires, Jeff Bezos and Elon Musk.
Mr Bezos plans to ride his own rocket, New Shepard, into space in nine days’ time.
Sir Richard is said to have pipped Mr Bezos to the post after moving forward his launch when the Amazon founder announced his own plans to enter space.
Elon Musk’s SpaceX is also in the running to monetise space travel.
Mr Musk’s company is currently the only operation with the capability of launching astronauts from US soil.
It has won a contract with NASA to build the next generation spacecraft that will return humans to the Moon.
Mr Bezos has raised questions about whether Sir Richard’s venture can actually be counted as space travel.
On Friday, Mr Bezos’ space company, Blue Origin, said anyone travelling on Sir Richard’s Unity spacecraft would not reach the “internationally recognised” altitude for where space begins - the so-called Kármán line of 100km.