Barney Platts-Mills was born in Colchester, and educated in London and Dorset before leaving school at 15 with hopes of becoming an actor. His father, Labour politician John Platts-Mills, was acquainted with producer and director Lewis Gilbert; Platts-Mills secured a job as third assistant trainee editor on Gilbert's The Greengage Summer (1961) at Shepperton Studios, where he also worked on Stanley Kubrick's Spartacus (1960), and John Schlesinger's A Kind of Loving (1962). He went on to edit on Anglia Television's Survival series and Granada Television's World In Action.
With a solid education in editing, Platts-Mills drifted out of television in search of a new challenge, and after a short break met Marlene and John Fletcher who, with their fledgling production company Dateline Films, were shooting a drama with boys from the Paddington Youth Club. Platts-Mills was introduced to the idea of an accessible, affordable, independent model of filmmaking, an ideal which would continue to influence his filmmaking practice. Through Dateline he was introduced to film director James Scott, and editor and cinematographer Adam Barker-Mill. In 1966 the three - all still only in their mid-twenties - set up Maya Films, bringing on board producer Andrew St. John.
Two short documentaries followed: Love's Presentation (1966, directed by Scott, produced and edited by Platts-Mills) on the work of David Hockney, and St Christopher (1967, directed and co-produced by Platts-Mills) on children in care in two Yorkshire schools, which received a screening in the House of Commons. Platts-Mills was then put in touch, again through his Dateline Films contacts, with Joan Littlewood, the innovative theatre director then in residence at the Theatre Royal in Stratford.
Littlewood wanted to make a documentary about her experimental drama work in East London. As a result Platts-Mills filmed Littlewood's work with a throng of local teenagers who - to dissuade them from delinquency and causing a nuisance outside the theatre - she would invite into her adjacent Playbarn, a vacant space where they were encouraged to improvise and play-act scenarios based on their everyday lives. In 1968, Platts-Mills completed his documentary about the group, Everybody's an Actor, Shakespeare Said.
Driven by the experience of Littlewood's working practice, and requests from the Playbarn boys that he make a 'proper film' with them, Platts-Mills went on to write and direct Bronco Bullfrog (1969), shot over six weeks on 35mm on a meagre £18,000 budget, on location in East London using a cast of non-professional actors. The film enjoyed critical acclaim on both sides of the Atlantic and won the Screenwriters' Guild Award for Best Screenplay in 1970.
Andrew St. John secured a £26,000 budget for their next project, Private Road (1971), written and directed by Platts-Mills, starring Bruce Robinson and Susan Penhaligon. The film was awarded a Golden Lion at the Locarno International Film Festival the same year. Platts-Mills recalls that the production - in colour, with a professional cast and a larger crew - was a conscious effort to fit with the more mainstream, commercial filmmaking model than Bronco was, and they determined to exploit it themselves. Concerned with distribution deals, financial returns and "ice cream sales", Platts-Mills acknowledges that he and St. John found themselves exhausted by the experience in spite of the popularity of the film with audiences.
Platts-Mills went on to write the screenplays Double Trouble, The Scotsman, Hero, and Ebb Tide. Double Trouble was published as a novel; Hero - a fable set in historic Scotland, shot in Gaelic using a Glasgow youth gang as actors - was made under Platts-Mills' direction for Channel Four in 1982. Pre-production began on Ebb Tide for Channel Four but the project was abandoned due to ongoing unrest in Sri Lanka, where it was to be filmed.
Platts-Mills was appointed a Governor of the BFI in 1972 but distanced himself from the mainstream industry, investigating instead the then-emergent reel-to-reel videotape technologies as a fast, affordable and portable way of filming. In the early 1970s he set up the Prodigal Trust, an inner-city project in London which encouraged schoolchildren to make videos. Through the late 1980s, he worked on video projects with prisoners in Glasgow (St. John had relocated to Glasgow after Private Road, working on a peoples' television project on the notorious Gorbals housing estate), before establishing Massive Videos in West London in 1993, a charitable company which took on commissions for films to be made by a group of trainees, largely made up of disadvantaged young people. In 1994 Massive Videos started the Portobello Free Film Festival, which in 2009 showed 800 new independent films. Massive Videos was wound up in 1999, and Platts-Mills is currently completing a new film, Zohra: A Moroccan Fairy Tale, a romance featuring the inhabitants of the North Moroccan village where he sometimes lives.