A hyperloop is a sealed tube system created to allow people to travel at speeds of hundreds of miles per hour.
Branson's company in September announced 10 finalist cities for its first installation, which it expects to build by 2021.
"I am excited by the latest developments at Virgin Hyperloop One and delighted to be its new Chairman" said Branson.
A 28-foot-long pod was placed into a 1,600-foot-long concrete test tube, which was depressurized to the equivalent air pressure experienced at 200,000 feet above sea level.
Musk recently tweeted that 10 purchasers of a hat bearing his company logo will be "picked at random" to tour his hyperloop tunnel in Los Angeles and drive his boring machine. "All components of the system were successfully tested including the airlock, highly efficient electric motor, advanced controls and power electronics, custom magnetic levitation and guidance, pod suspension, and the vacuum".
In the summer, the company sent a pod about 192 miles per hour.
Virgin Hyperloop One said on Monday it has raised $50 million in new financing and named Richard Branson, founder of the Virgin Group, as its non-executive chairman.
"The recent phase three testing continues to prove the incredible persistence and determination of our DevLoop team - the close to 200 engineers, machinists, welders, and fabricators who collaborated to make hyperloop a reality today".
Mr Branson's appointment as non-executive chairman comes two months after the Virgin Group announced an undisclosed investment in the company, which was renamed to include reference to the Virgin Brand.
Virgin Hyperloop One is one of a handful of firms developing technologies in which passengers and cargo can be loaded into pods that travel at high speeds through low-friction tubes above or below ground.
On Monday Virgin Hyperloop One announced a new record for its prototype pod-387kph (or 240mph).