The World War I drama, which stars Jeremy Irvine, Tom Hiddleston and Benedict Cumberbatch, pulls in £3.2 million in ticket sales to secure the number one spot for the second consecutive weekend.
Action movies Haywire and Underworld: Awakening battled it out for second place, with Steven Soderbergh's espionage film taking £1.19 million against £1.11 million for Kate Beckinsale's vampire sequel.
Sherlock Holmes: A Game of Shadows and Meryl Streep's The Iron Lady complete the top five.
Jonah Hill comedy The Sitter debuts at number six with £910,382 from 355 screens.
The Artist has now earned more than £3 million from UK cinemagoers.
Elsewhere, Clint Eastwood's J. Edgar and W.E. fail to dent the top ten as they debut at numbers 12 and 14 respectively. The latter, Madonna's first major film as a director, grosses £182,914 from 172 screens.
The UK box office top ten in full:
1. (1) War Horse - £3,202,493
2. (-) Haywire - £1,197,866
3. (-) Underworld: Awakening - £1,114,327
4. (3) Sherlock Holmes: A Game of Shadows - £956,434
5. (2) The Iron Lady - £949,517
6. (-) The Sitter - £910,382
7. (4) Mission: Impossible - Ghost Protocol - £815,330
8. (7) The Artist - £770,403
9. (8) Alvin and the Chipmunks: Chipwrecked - £568,758
10. (9) Puss in Boots - £568,590
Watch Hollywood stars reveal their favourite film from War Horse director Steven Spielberg below: