The US pop singer - real name Stefani Germanotta - also lands in the top three of the albums chart this week with her debut disc The Fame.
The highest new entry on the singles countdown comes from US rapper Kid Cudi, who bows at two with debut release 'Day 'N' Nite'.
James Morrison and Nelly Furtado slip to three with 'Broken Strings', while The Saturdays climb from six to four with 'Issues'.
Meanwhile, Girls Aloud notch up their 20th consecutive top ten hit after leaping from 29 to ten with 'The Loving Kind'.
Outside of the top ten, Britney Spears advances from 24 to 17 with 'Circus', while Alesha Dixon climbs from 39 to 23 with 'Breathe Slow'.
The top ten singles in full (click to read our reviews):
1. (1) Lady GaGa ft. Colby O'Donis: 'Just Dance'
2. (-) Kid Cudi vs. Crookers: 'Day 'N' Nite'
3. (2) James Morrison ft. Nelly Furtado: 'Broken Strings'
4. (6) The Saturdays: 'Issues'
5. (10) Kevin Rudolf ft. Lil Wayne: 'Let It Rock'
6. (3) Alexandra Burke: 'Hallelujah'
7. (8) Beyoncé: 'Single Ladies (Put A Ring On It)'
8. (5) Kings of Leon: 'Use Somebody'
9. (4) Leona Lewis: 'Run'
10. (29) Girls Aloud: 'The Loving Kind'
Source: Official Chart Company
> Click here for this week's top ten albums