The singer extends her reign at number one for a sixth non-consecutive week with the track, while Miley Cyrus moves from three to two with 'Wrecking Ball'.
Meanwhile, James Blunt is the highest new entry at five with 'Bonfire Heart', Lorde's 'Love Club' EP rebounds from 14 to six, and Nathaniel Willemse's 'You' debuts at number nine.
Further down the chart, Avicii starts at 14 with 'Hey Brother', Jason Derulo shifts from 28 to 15 with 'Marry Me', and Zedd and Hayley Williams vault from 32 to 16 with 'Stay The Night'.
Ylvis move from 29 to 19 with 'The Fox', Justin Bieber's 'Heartbreaker' is new at 30, and Havana Brown lands at 32 with 'Warrior'.
Elsewhere, Mike WiLL Made It and Cyrus enter at 39 with '23', and The X Factor Australia's Taylor Henderson bows at 49 with his rendition of 'Wake Me Up'.
1. (1) Katy Perry: 'Roar'
2. (3) Miley Cyrus: 'Wrecking Ball'
3. (4) Redfoo: 'Let's Get Ridiculous'
4. (2) Jessica Mauboy: 'Pop A Bottle (Fill Me Up)'
5. (*) James Blunt: 'Bonfire Heart'
6. (14) Lorde: 'The Love Club' EP
7. (11) Avicii: 'Wake Me Up'
8. (5) Jason Derulo ft. 2 Chainz: 'Talk Dirty'
9. (*) Nathaniel Willemse: 'You'
10. (9) Drake: 'Hold On, We're Going Home'
Watch the music video for 'Roar' below: