Mayor of London Sadiq Khan said the "heartbreaking" pictures of a bloodied lesbian couple attacked on a night bus showed the importance of Pride as he launched the parade.
Mr Khan said the "huge, huge progress" in gay rights should be celebrated, but added "we must never be complacent".
This parade is aiming to champion diversity, with the introduction of a new World Area at Golden Square in Soho.
Organisers hoped it will to increase the visibility of black, Asian and minority ethnic (Bame) LGBT+ people.
Hundreds of officers will police the parade, and Scotland Yard has advised people to stay vigilant while enjoying the day.
The parade will begin at midday from Portland Place and finish on Whitehall.
Commander Helen Millichap said: "We want Pride to be a friendly and safe event for everyone to enjoy.
"We need the public to help us by taking the usual precautions by remaining vigilant and reporting anything of concern to police officers or stewards at the event."
"As with any large event, the Met's priority is public safety and we are working closely with the organisers in the lead-up to Pride to develop our policing plan".
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