Parade director Christopher Joell-Deshields said this year's event was the most diverse yet.
He added: "It's just a day to be proud of really - people are able to just come and be who they are and celebrate whatever they want."
About 30,000 people from 472 organisations marched through the centre of the capital for the annual parade.
Among those was campaigner Laks Mann, of the group Gaysians.
"We are a group supporting the Asian LGBT community," he said. "We launched last year at Pride - I just felt that we needed to come together and have a unified voice."
Crowds cheered as the parade got under way with a huge rainbow flag in Regent Street.
Mayor of London Sadiq Khan was at the event and it was also the first time uniformed officers from the Royal Marines took part in the parade.
Thousands of supporters lined the streets, which were filled with balloons, sequins and flags.
The NHS took centre stage with a banner at the front of the march with the parade coinciding with the health service's 70th anniversary.