Dressed in a black, sequinned leotard and thigh-high stockings, the pop star appeared at Brighton Pride on stage on Saturday night waving the LGBT symbol during the encore of her headline act before blowing kisses to the crowd.
Organisers anticipated up to 100,000 fans would flood in to Preston Park to watch the biggest act ever to perform at the event as she brought her Las Vegas Piece of Me show to the East Sussex city.
The performance kick starts her Europe tour and marks her first time on stage on UK soil since 2011.
The tour is set to finish at the Tower Festival Headland on the Promenade in Blackpool on Saturday, September 1.
Crowds were treated to a rollercoaster ride through her back catalogue, which left them chanting the songs as they left the site and calling for more.
Ahead of the show the singer - described as an "ally of the gay community" - told Twitter followers she was looking forward to sharing love and equality at the event.
Members of the audience could be overheard describing the 36-year-old singer as the "comeback queen" as she offered them a classic Britney production - full of slick routines with around 20 backing dancers and several costume changes in an hour-and-a-half set.
Renditions of Baby One More Time and Oops!... I Did It Again prompted huge cheers but it was Toxic, Stronger and (You Drive Me) Crazy that attracted the loudest roars from the crowd.
During the whirlwind set, songs including Boys, Me Against The Music, Piece of Me, Gimme More, Womaniser, If You Seek Amy, Do Somethin', Scream and Shout, Circus, were also performed.
Appearing in black glitter-clad lingerie, she also attracted screams and cheers while she danced up against a pole while singing I'm A Slave 4 U, and when she tied a leash around the member of a crowd who was picked to dance with her on stage.
Part of her routine included a tribute to songs by rapper Missy Elliott.
The singer returns to the UK in two weeks with a performance in Scarborough.