At least 50 people were killed and dozens injured after 29 year-old Omar Mateen attacked a gay club in Florida on Sunday.
Thousands of England's lesbian, gay, bisexual and transgender (LGBT) communities gathered in London's Soho district. Vigils and memorials were also held in other towns and cities including Manchester, Leicester, Brighton and Nottingham.
The Pride flag was flown at half mast from City Hall in memory of those killed in the shooting in deadliest attack in US history.
"The capital stood "shoulder to shoulder" with Orlando, ahead of vigils around the country,"Mayor Sadiq Khan was quoted as saying.
Vigil in Soho was held outside the Admiral Duncan pub in Old Compton Street, Soho, where three people died and many more were injured in a bomb attack in 1999.