The 3D film, which centres on a flame-haired princess (Kelly Macdonald) growing up in Scotland, pulls in £5.2 million to hold off competition from The Bourne Legacy and secure the top spot.
Brave expanded from Irish and Scottish theatres into England and Wales over the weekend, prompting a huge 818% leap in ticket sales.
Seth MacFarlane's comedy Ted is in third place ahead of new release The Expendables 2. Sylvester Stallone's action sequel falls short of its predecessor, which netted £3.94 million when it opened in 2010.
Last week's runner-up The Dark Knight Rises falls three places to number five.
Elsewhere, Bollywood film Ek Tha Tiger charts at number six and Rufus Hound's comedy The Wedding Video lands at ten.
The UK box office top ten in full:
1. (5) Brave - £5,269,402
2. (-) The Bourne Legacy - £4,620,289
3. (1) Ted - £2,076,046
4. (-) The Expendables 2 - £1,985,082
5. (2) The Dark Knight Rises - £1,506,178
6. (-) Ek Tha Tiger - £543,073
7. (4) Diary of a Wimpy Kid: Dog Days - £459,526
8. (6) Ice Age 4: Continental Drift - £350,788
9. (3) Step Up 4: Miami Heat - £340,072
10. (-) The Wedding Video - £333,079
Photo gallery - Pixar at the movies: