The result marks the 20th song in the chart's history to enter in pole position, as well as the singer's seventh number one on the tally since her debut 'I Kissed A Girl' hit the top in 2008.
Meanwhile, Whitney Houston leaps seven to three with 'I Will Always Love You', Adele's 'Rolling in the Deep' rebounds 17 to five following her Grammys performance and 'Someone Like You' lifts from 11 to seven.
Elsewhere, Nicki Minaj debuts at nine with 'Starships', and Chris Brown lands at ten with 'Turn Up The Music'.
Further down the chart, Selena Gomez reaches a new peak with 'Love You Like A Love Song', which rises from 30 to 22, and One Direction's 'What Makes You Beautiful' starts at number 28.
Bruno Mars enters at 50 with 'Runaway Baby', Adele's 'Rumour Has It' re-enters at 67, and David Guetta, Chris Brown and Lil Wayne's 'I Can Only Imagine' is at 90.
The Top 10 singles in full (click where possible for our reviews):
1. (*) Katy Perry: 'Part of Me'
2. (2) Adele: 'Set Fire to the Rain'
3. (7) Whitney Houston: 'I Will Always Love You'
4. (1) Kelly Clarkson: 'Stronger'
5. (17) Adele: 'Rolling in the Deep'
6. (3) fun. ft. Janelle Monae: 'We Are Young'
7. (11) Adele: 'Someone Like You'
8. (6) Rihanna ft. Calvin Harris: 'We Found Love'
9. (*) Nicki Minaj: 'Starships'
10. (*) Chris Brown: 'Turn Up The Music'
Listen to Katy Perry's 'Part of Me' below: