Photographers and film-makers Kris Reid and Marty Bell, who grew up in the Highlands, and Sheffield-born Tom Welsh launched Tens in 2014.
They initially raised money for the business through crowdfunding.
The investment from Virgin Group founder, Sir Richard, will be used to promote sales of Tens overseas.
At the moment, the UK is the largest market for the product.
The three friends have not disclosed the value of Sir Richard's investment, but said it was "significant".
Mr Bell, from Inverness, Mr Reid, who is also from Inverness and grew up in Beauly, and Mr Welsh met while studying at Napier University in Edinburgh.
They came up with the idea to create their own sunglasses brand on a road trip in the Scottish Highlands.

Nasa has created Mars Trek to mark the third anniversary of the rover landing on Mars.
It allows people to see for themselves some of the features of the red planet using information gathered by Nasa over the past 50 years.
A team from Nasa is also using the interactive map to look at possible landing sites for future missions.
A sunglasses brand founded by three friends in the Scottish Highlands and now based in Glasgow has secured investment from Sir Richard Branson.
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Nasa has created a new interactive web site to allow people to explore the surface of Mars just like the Curiosity rover is doing.