The first chapter of Peter Jackson's new Middle-earth trilogy continued to fend off competition from Ang Lee's Life of Pi and the Tom Cruise-starring Jack Reacher.
The Hobbit made a weekend total of £6.8 million from its 596 locations, outstripping Life of Pi's second-place gross of £4.1 million from 550 locations.
Jack Reacher debuted at number three with a weekend total of £3,575,066.
The top ten's other new entry was Billy Crystal-starring comedy Parental Guidance, which debuted at number five with £1,293,400.
Skyfall fell to seventh place, having this week become the first James Bond movie to earn over $1 billion at the worldwide box office.
Musical comedy Pitch Perfect climbed one place to number four, while DreamWorks' Rise of the Guardians fell from number three to number six.
The biggest fall was claimed by festive sequel Nativity 2: Danger in the Manger, which went from fourth place to ninth.
The UK box office top ten in full:
1. (1) The Hobbit: An Unexpected Journey - £6,850,728
2. (2) Life of Pi - £4,180,308
3. (-) Jack Reacher - £3,575,066
4. (5) Pitch Perfect - £1,295,355
5. (-) Parental Guidance - £1,293,400
6. (3) Rise of the Guardians - £1,022,539
7. (6) Skyfall - £890,022
8. (7) Tinker Bell and the Secret of the Wings - £623,067
9. (4) Nativity 2: Danger in the Manger - £386,248
10. (9) The Twilight Saga: Breaking Dawn - Part 2 - £250,281
Watch Martin Freeman speaking to Digital Spy about The Hobbit below: