Westwood, who is famous for her punk designs, wore a T-shirt with the words "I am Julian Assange" next to a picture of her own face, the Daily Telegraph reported.
She also wore the T-shirt when she closed her recent London show to express her support for the controversial Australian, who has been holed up in the embassy since this June to avoid extradition to Sweden where he is wanted for questioning over claims of sex offences.
Assange and his supporters claim that they fear that Sweden would send him to the US where he could face the death penalty.
British police have said they would arrest the WikiLeaks founder should he leave the embassy.
Other prominent entertainment personalities that have come out in support of Assange include directors Michael Moore and Oliver Stone.
Assange has already attracted entertainment industry with some film and TV projects set to depict his life.
