In a statement, the company said Macpherson would be advising and assisting with future product development, brand positioning and sales strategy.
Chairman Ranjit Murugason said Macpherson would bring a 'dynamic dimension and appreciation of developments in surf and youth fashion', as well as 'boosting the awareness of Hot Tuna as a brand'.
Macpherson added: 'I believe this to be a maverick and dynamic union.'
The supermodel has signed a two-year contract and will take up the post with immediate effect. She will not be working with the company full-time, but will attend all board meetings and be present at strategic and management meetings.
Macpherson will be granted shares and options worth more than£2 million. She currently runs a lingerie line - Elle Macpherson Intimates - and a beauty range sold at Boots.
The company, predominantly a wholesale business, plans to open its first London flagship store next year. It was floated on AIM last September.