The British entrepreneur, along with two pilots and three other passengers, is due to begin his mission onboard the space plane VSS Unity at around 7am local US time (2pm BST) on Sunday.
The plane will fly to where the sky turns black and the Earth’s horizon curves away into the distance, before experiencing several minutes of weightlessness and returning to the company’s New Mexico launch headquarters.
A livestream can be viewed here on Virgin Galactic’s YouTube page.
It will be the first time that the company has conducted a fully crewed flight to the edge of space, though not the first time people have travelled in the spacecraft.
Mr Branson had not originally been due to ride on VSS Unity for test flights, but Virgin Galactic confirmed his participation has been expedited so he could “test the private astronaut experience”.
The spaceplane’s two pilots, Dave Mackay and Michael Masucci, will control the ignition and shutoff of the ship’s rocket engine, and activate the vehicle’s “feathered” tail maneuver for re-entry.
The three other mission specialists are Beth Moses, the company’s chief astronaut instructor; Virgin Galactic‘s lead operations engineer Colin Bennett; and Sirisha Bandla, a research operations and government affairs vice president.
“I’ve always been a dreamer. My mum taught me to never give up and to reach for the stars. On 11 July, it’s time to turn that dream into a reality aboard the next @VirginGalactic spaceflight,” tweeted Mr Branson.
It will be Virgin Galactic’s fourth crewed test flight using VSS Unity, a spaceplane that is dropped from a carrier in mid-air before shooting up to the very edge of space.
Assuming the mission goes well, Virgin has said it plans two further test flights of the spaceplane before beginning commercial service next year.
The company has said it has received more than 600 flight reservations, priced at around $250,000 per ticket, but hopes eventually to slash the cost of each seat to $40,000.
Mr Branson’s decision to board the space plane followed the announcement by Amazon founder Jeff Bezos that he would be onboard his company Blue Origin’s flight on 20 July.
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.
Mr Branson has denied it is a race, despite announcing his plan soon after Bezos and scheduling a date shortly before.
“It’s honestly not a race,” Branson told Reuters. “If it’s a race, it’s a race to produce wonderful spaceships that can make many more people be able to access space. And I think that’s both of our aims.”
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