Directed by Clint Eastwood and starring Bradley Cooper as Navy Seal Chris Kyle, the film has taken $337.2m (£223.7m) since its limited release in December.
The latest movie in The Hunger Games franchise has taken $336.8m (£223.4m).
Set during the Iraq war, American Sniper is Eastwood's most successful film to date.
The film had a limited release in US cinemas on 25 December, to make it eligible for this year's Oscars. A wider release followed in January.
According to Variety, it is the first time since 1998's Saving Private Ryan that a "realistic", R-rated drama has secured the largest box office takings of the year in the US.
"The heroic story of Chris Kyle just hit the zeitgeist," said Jeff Goldstein, from film company Warner Bros.
American Sniper was nominated for six Oscars, including best picture and best actor for Cooper, but only won in the sound editing category.
Despite its popularity with US cinemagoers, the film attracted criticism for both its depiction of the Iraq war and of sniper Chris Kyle, upon whose book the film is based.
Globally, Transformers: Age of Extinction is still the biggest film of 2014 having taking $1.1bn (£665.6m) in foreign markets, compared to American Sniper's $140m (£93m).
Robot drama Chappie made its debut at the top of this week's US box office after an unusually quiet weekend, in which takings were 38% down on the same time last year.
Neill Blomkamp's film, starring Hugh Jackman, Dev Patel and Sigourney Weaver, took just $13.3m (£8.8m) but still topped this week's chart.
Blomkamp's previous two films, Elysium and District 9, debuted much higher, with $29.8m (£19.8m) and $37.4m (£24.9m) respectively.
Will Smith's Focus took $10m (£6.6m) in its second week, with The Second Best Exotic Marigold Hotel - also starring Dev Patel - opening in third place with a strong $8.6m (£5.7m).
Unfinished Business, Vince Vaughn's new comedy, opened in 10th place with just $4.8m (£3.2m).
American Sniper has beaten The Hunger Games: Mockingjay - Part 1 to become the highest-grossing film release of 2014 in the US.