The only ferry linking Hayling Island to Portsmouth closed down in 2015 when the company went into administration.
The firm's collapse left about 70 schoolchildren and commuters facing a 16-mile road journey instead of a three-minute ride to Eastney.
Sir Richard was approached for support after taking part in an annual Hayling Island  kitesurfing festival.
The entrepreneur's Virgin group sponsors the event, which runs this year from 17-19 June.
The 200-year-old ferry service collapsed in March 2015.
The company was then sold to Baker Trayte Marine Ltd but the new owner's plan to restore the service stalled when Hampshire County Council said it could no longer justify an annual subsidy. The service cost the authority £71,000 in 2014.
The newly-launched Hayling Ferry Trust, led by local councillor Clare Satchwell, said it aimed to raise a total of £40,000 to support the new private operator.
Ms Satchwell said: "It's like a phoenix from the flames. We want to harness public positivity... and Sir Richard's donation is a real boost."
Sir Richard Branson has donated £5,000 to help re-establish a ferry service in Hampshire.