He joins Jane Giles, who as recently reported has come to the BFI as head of content.
Dunn had been in the home entertainment division at Tartan Films for seven years. He most recently served as Deputy Managing Director.
Giles had been head of acquisitions at Tartan UK and US and she is also a veteran of ICA Cinemas, Channel 4 and the London Film Festival. She previously worked at the BFI as head of distribution.
Heather Stewart, Cultural Programme Director of the BFI, said: 'We are very happy that two such strong talents are coming to the BFI. Jane joins us at a critical moment in a changing multi-platform world, bringing new thinking about how we can reach new audiences. Sam brings great experience and knowledge to develop our DVD label and meet our high sales targets.'