The singer's global hit 'Happy' spends a seventh week atop the Irish singles chart, while Clean Bandit's 'Rather Be' sits at two.
Pitbull and Ke$ha are at three with 'Timber', Hozier climbs back up to four with 'Take Me To Church' and Avicii slips to five with 'Hey Brother'.
Idina Menzel's 'Let It Go' from the Disney movie Frozen advances to 13, David Guetta lands at 18 with new single 'Shot Me Down' and London Grammar's 'Strong' vaults up to 23.
Vance Joy's 'Riptide' leaps from 46 to 27, Ellie Goulding's 'Goodness Gracious' begins to climb at 41 and Disclosure are at 52 with the Mary J Blige version of 'F For You'.
The Irish singles top ten appears below (click where possible for reviews):
1. (1) Pharrell Williams: 'Happy'
2. (2) Clean Bandit: 'Rather Be'
3. (3) Pitbull ft. Ke$ha: 'Timber'
4. (6) Hozier: 'Take Me To Church'
5. (4) Avicii: 'Hey Brother'
6. (5) Ellie Goulding: 'How Long Will I Love You'
7. (9) Shakira ft. Rihanna: 'Can't Remember To Forget You'
8. (15) Zedd ft. Hayley Williams: 'Stay The Night'
9. (11) Katy Perry: 'Dark Horse'
10. (8) Jason Derulo: 'Trumpets'
Watch the music video for Pharrell's 'Happy' below: