The actress topped the magazine's annual 100-name list, beating Rihanna into second place.
> Helen Flanagan, Pendleton at 'FHM' 100 Sexiest Women party - pictures
> Ten Things About... Mila Kunis
The top British entry was Helen Flanagan, while the top five was rounded out by fellow Brits Michelle Keegan and Kelly Brook.
FHM 100 Sexiest Editor Dan Jude said: "Mila Kunis has had a phenomenal year - she's starred in the highest-grossing comedy [Ted] and is the most in-demand Hollywood star right now.
"Not only is she naturally stunning, but she has a great sense of humour and isn't afraid to poke fun at herself.
"The nation has spoken, and the verdict is that she is officially the perfect girlfriend. She'll take some beating in 2014."
Kunis was voted Digital Spy readers' top Valentine's Day date earlier this year, having already been named the sexiest female celebrity of 2012 last December.
She was also named Esquire's 'Sexiest Woman Alive' last October.
Of being the highest-placed Briton in the poll, Flanagan said: "I'm absolutely thrilled to be voted the Sexiest Woman in the UK.
"It's a lovely confidence boost, especially when there are so many beautiful girls out there. Rosie Webster would definitely be impressed!"
Last year's winner Tulisa Contostavlos dropped just outside the top ten, to 11th place.
27% of this year's list are older than 30, including Splash! star Linda Barker, 51, at number 93.
FHM 100 Sexiest - the top 20:
1. (9) Mila Kunis
2. (3) Rihanna
3. (47) Helen Flanagan
4. (26) Michelle Keegan
5. (20) Kelly Brook
6. (56) Kaley Cuoco
7. (12) Pixie Lott
8. (23) Kate Upton
9. (2) Cheryl Cole
10. (5) Georgia Salpa
12. (99) Taylor Swift
13. (86) Jorgie Porter
14. (4) Rosie Jones
15. (94) Rita Ora
16. (6) Katy Perry
17. (7) Megan Fox
18. (14) Mollie King
19. (38) Beyonce
20. (74) Jennifer Lawrence
Stars who have dropped out of the list include Abbey Clancy, Paris Hilton, Angelina Jolie, Adriana Lima and Duchess of Cambridge Kate Middleton, while her sister Pippa is at number 58
Jennifer Aniston dropped out of the list in 2011 for the first time since 1996, but re-entered last year at 79 and rose to 34 in this year's list.