After two years of cancellations because of the coronavirus pandemic, the parade came half a century after Britain's first march to celebrate Pride in 1972 in London.
Saturday's procession took on a similar route to the original, starting outside Hyde Park and touring the streets towards Westminster.
The London mayor's office said that more than one million revelers attended the celebrations, which also included a concert in Trafalgar Square.
Chris Joell-Deshields, the director of organisers Pride in London, said "momentous" rights and freedoms had been earned since the inaugural event, "but there is more to be done".
London Mayor Sadiq Khan hailed a "beautiful day" of "unity, visibility, equality and solidarity" as he joined in the celebrations.
More than 600 LGBTQ groups were expected to take part in the march, which was headed by members of the Gay Liberation Front from the 1972 protest.
Organisations ranging from charities to universities to the emergency services were also represented. But uniformed officers from London's Metropolitan Police force weren't among them, as has been the case in previous years.
The move came in response to LGBTQ campaigners raising concerns over their confidence in policing, in particular the quality of the police force's investigation into murders carried out by serial killer Stephen Port.
In 2016, Port was sentenced to life in prison without parole for the murders of four young gay men whom he met online.
Members of the police force were able to join Saturday's march of their own accord.
"I think the police have been sensitive to the issues raised by the community," Khan said. "And there will be uniformed officers in and around Pride to make sure we're all safe, to make sure this parade is a success."
Those taking part had been urged to take a COVID-19 test before the march with virus cases on the rise across Britain.
The UK Health Security Agency had issued a similar caution for people showing possible symptoms of monkeypox.
