The model and designer unveiled 147 union flags including 10 dedicated fashion flags to celebrate Great British fashion to fly 90 feet high above the iconic street.
The flags will represent the 147 years since Oxford Street was made into a modern high street, and will also mark the Queen's upcoming Diamond Jubilee.
The showcase will run for six weeks over the summer, and will be the first of 500 flags across London's West End including Bond Street, Regent Street and Piccadilly Circus.
Guinness said of the celebration: "We love Oxford Street, it's the centre of London. It's what makes London glamorous."
The unveiling ceremony was supported by the British Fashion Council and the Government's GREAT campaign.
The Minister for Tourism and Heritage, John Penrose MP also attended the ceremony to celebrate the British fashion industry, which contributes over £2 billion a year to the UK economy and helps create around 1.31 million jobs.
Watch Jasmine Guinness launch the showcase below: