The film follows Perry during her 'California Dreams' worldwide tour.
Perry arrived with a Union Flag umbrella as she braved the wet weather on the red carpet.
Conor Maynard, blogger Perez Hilton and comedian Russell Kane were among the celebrity guests who attended tonight's premiere in London's Leicester Square.
The concert documentary starring the 'Teenage Dream' singer is released at cinemas on July 5.
In pictures - the London premiere of Katy Perry: Part of Me:
Copyright: PA Images Ian West/PA WireWatch an exclusive Digital Spy clip from the movie below: