Amma Asante's A United Kingdom, about a British woman falling in love with an African king, stars British actors Rosamund Pike and David Oyelowo.
Festival director Clare Stewart said her selection better reflects society at a time the film business is seen as being too white and male.
The industry needs to be "mindful of audiences", she told the BBC.
"We have a very diverse audience and the stories we bring to the screen should be reflecting that audience."
Asante's film tells the story of Seretse Khama, King of Bechuanaland - now modern Botswana - and Ruth Williams, the London office worker he married in 1948 and the opposition they faced from their families and their own countries.
In total, 74 countries are being represented at the 60th London Film Festival, which runs until 16 October.  Some 245 films are featured over the 12 days, including 18 world premieres.
Stars including Amy Adams, Jeremy Renner, Sigourney Weaver, Casey Affleck, Michelle Williams and Nicole Kidman are set to attend.
Oyelowo is appearing in another high-profile film, Queen of Katwe, also starring Oscar-winner Lupita Nyong'o, which has its premiere on Sunday.
The LFF will feature the European premiere of slave drama The Birth of a Nation, about Nat Turner's 1831 rebellion.
Actor and director Nate Parker, who has faced recent media scrutiny over a historic rape trial, will be in London for the screening.
The British Film Institute is also hosting a Black Star symposium to highlight the difficulties faced by black actors.
There will also be gala premieres for Oliver Stone's Snowden, about the NSA whistleblower, designer Tom Ford's Nocturnal Animals, Oscar-tipped musical La La Land, which stars Emma Stone and Ryan Gosling, and Manchester by the Sea, a family drama set in Massachusetts starring Michelle Williams and Casey Affleck.
The festival will close with Ben Wheatley's Free Fire, his follow-up to High Rise which features Brie Larson and Cillian Murphy.
A 780-seat pop-up cinema has been erected in Victoria Embankment Gardens as part of the festival.
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The BFI London Film Festival will launch later with a film directed by a black woman opening it for the first time.