Premier won a competitive pitch against three other agencies, including incumbent agency of five years, Dennis Davidson Associates.
In a refashioning of its external PR handling, the RLFF - which is run by the festivals arm of the British Film Institute (bfi) - has hired separate agencies for event management.
Premier sister firm Beatwax Communications is to handle events work for sponsored screenings, while Freud Communications will handle event and media management for the opening and closing galas.
The 46th RLFF will be held from 6-21 November at London cinemas such as the Odeon West End and the National Film Theatre on the South Bank.
It will feature around 180 feature films and 70 short films from more than 40 countries.
A nationwide tour of around two weeks will follow the London festival, calling in around eight towns and cities.
Premier director Ginger Corbett leads various teams on the account, reporting to bfi marketing head Andy Cole, RLFF artistic director Sandra Hebron, bfi sponsorship head Lottie Wake and RLFF executive director Adrian Wootton.
At Beatwax, MD Chris Ward heads the work, with director of film Kate Lee heading Freuds' account team.
Premier will manage the RLFF's press office and virtual press office, co-ordinate press screenings and handle accreditation.
International film-makers and press will be targeted by an extensive media relations campaign, as will ethnic minority newspapers in the UK.