As part of the partnership, Brightline will leverage the Virgin brand and marketing expertise for its current and upcoming developments.
Brightline will also rename itself as Virgin Trains USA this month and is expected to carry out the transition to new branding next year.
Virgin Group founder Richard Branson said: “Tens of millions of Americans travel on the railways every day, and we have tried for over a decade to find an opportunity to provide them with that same excellent service experience.
“Brightline is at the forefront of innovation in this market and the ideal partner for Virgin to work with to alter perceptions and travelling habits across the US.”
Under the partnership, an affiliate of Virgin Group has agreed to make a minority investment in Brightline. The agreement is subject to certain closing conditions.
Following the completion of the deal, funds managed by an affiliate of Fortress Investment Group will retain majority stake in Brightline.
Brightline’s existing management team will supervise the day-to-day operations, engineering, business development and strategy of the company.
Brightline president Patrick Goddard said: “This partnership further validates the incredible accomplishments of our team as we challenge conventional wisdom to reinvent train travel in America.
“Given our shared values and Virgin’s track record, this partnership will help amplify our efforts and growth potential as we seek to expand to new markets.”
In May, Brightline launched a passenger rail service in Florida, US, between Miami, Fort Lauderdale and West Palm Beach.
The company unveiled its plans to develop an intercity passenger rail system between Las Vegas and Southern California in the US.