The girl group's X Factor winner's single 'Cannonball' fought off competition from Olly Murs's 'Dance With Me Tonight', which advances to number two.
Rihanna's 'We Found Love' moves up to number three, while Coldplay's 'Paradise' slips to four and Flo Rida's 'Good Feeling' sits at five.
Outside the top ten, Avicii's 'Levels' remains at 11, Lloyd jumps eight places to 18 with 'Dedication To My Ex (Miss That)' and Adele's 'Someone Like You' moves up to 21.
JLS's latest single 'Do You Feel What I Feel?' debuts at number 29, while Jessie J's new single 'Domino' lands at 35.
This week's Irish Top 10 is as follows:
1. (1) Little Mix: 'Cannonball'
2. (3) Olly Murs: 'Dance With Me Tonight'
3. (4) Rihanna feat. Calvin Harris: 'We Found Love'
4. (2) Coldplay: 'Paradise'
5. (7) Flo Rida: 'Good Feeling'
6. (5) Ed Sheeran: 'Lego House'
7. (12) Florence + The Machine: 'Shake It Out'
8. (10) LMFAO: 'Sexy And I Know It'
9. (19) Lana Del Rey: 'Video Games'
10. (13) Maroon 5 feat. Christina Aguilera: 'Moves Like Jagger'
Watch the music video for Little Mix's 'Cannonball' below: