Tom Hooper's musical, starring Hugh Jackman, Anne Hathaway and Russell Crowe, pulls in more than £8 million to end The Hobbit's four-week run at the chart summit.
The film's opening haul makes it the highest-grossing musical opening ever in the UK, topping the £6.59 million earned by Mamma Mia! in 2008.
Life of Pi climbs up the chart to second place ahead of new release Gangster Squad, while The Hobbit slips to number four. The Impossible rounds out the top five.
Elsewhere, horror remake Texas Chainsaw 3D debuts at number six with £1.2 million.
The UK box office top ten in full:
1. (-) Les Misérables - £8,127,991
2. (3) Life of Pi - £2,339,593
3. (-) Gangster Squad - £2,090,614
4. (1) The Hobbit: An Unexpected Journey - £1,861,157
5. (2) The Impossible - £1,859,505
6. (-) Texas Chainsaw 3D - £1,247,735
7. (4) Quartet - £891,829
8. (5) Jack Reacher - £690,043
9. (6) Pitch Perfect - £453,205
10. (7) Parental Guidance - £401,627
Watch Digital Spy speak to the stars of Les Misérables below: