The girl group fought off competition from Coldplay's 'Paradise', which advanced a few places to settle at this week's number two.
Olly Murs's 'Dance With Me Tonight' climbs to number three, Rihanna's 'We Found Love' is at four and Ed Sheeran's 'Lego House' completes the top five.
Maroon 5's 'Moves Like Jagger' vaults ten places to 13, while Rihanna makes a second appearance with her new single 'You Da One' at 17.
Further down the chart, The Wanted's 'Warzone' debuts at number 27, while Beyoncé's 'Best Thing I Never Had' re-enters at 37.
This week's Irish Top 10 is as follows:
1. (1) Little Mix: 'Cannonball'
2. (4) Coldplay: 'Paradise'
3. (5) Olly Murs: 'Dance With Me Tonight'
4. (6) Rihanna feat. Calvin Harris: 'We Found Love'
5. (10) Ed Sheeran: 'Lego House'
6. (3) Sara Bereilles & Ingrid Michaelson: 'Winter Song'
7. (12) Flo Rida: 'Good Feeling'
8. (7) Ryan Sheridan: 'Walking In The Air'
9. (15) One Direction: 'What Makes You Beautiful'
10. (19) LMFAO: 'Sexy And I Know It'
Watch the music video for Little Mix's 'Cannonball' below: