The announcement was made as 49-year-old Malhotra presented a preview of his latest festive collection as part of a charity event for the Trust.
"We are very excited to have Manish on board as an ambassador for the trust," said Hitan Mehta, executive director of the British Asian Trust.
"It has been great celebrating and showcasing the best of the Indian fashion industry that is Manish Malhotra and at the same time raising the awareness and funds to help those disadvantaged in South Asia," he added.
The event was held last week at one of the UK's newest Indian high fashion multi-brand store Aashni + Co in central London.
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Aashni Anshul Doshi, founder and creative director of Aashni + Co, added: "It's been wonderful, with an amazing response to Manish's new collection as well as to the news of his ambassadorship for the British Asian Trust."
In 2007 Prince Charles, the heir to Britain's throne, had turned to the entrepreneurial spirit of the British-Asian diaspora, aiming to link them up with innovative social entrepreneurs and grassroots organisations in the region.
It has touched the lives of over three million people in South Asia by connecting up with a number of grassroots organisations.