Roger Graef, the documentary maker, theatre director and writer who has died aged 85 of cancer, played a major part in holding the criminal justice system to account and was instrumental in changing the ways that victims of rape and domestic violence were treated by the police.

He also had a distinguished record in showing the inner workings of organisations ranging from the US Senate and the European Union to the British Communist party and British Steel, and of highlighting injustices, whether in the treatment of children in care or the destruction of our towns and cities.

His “fly-on-the-wall” style and his open and genial manner helped him win the trust of the subjects of his many films for the BBC, Granada Television, Channel 4 and ITV in a career spanning more than six decades. His interest in crime and justice led to more than 30 related programmes, including the influential In Search of Law and Order, an investigation into the treatment of young offenders in both the US and UK. His remarkable body of work led to him being the first documentary maker to be awarded a Bafta fellowship for lifetime achievement.

Born in New York, the son of Gretchen (nee Waterman) and Irving Graef, a doctor, Roger was educated at Horace Mann, a private school in the Bronx, and the progressive Putney school in Vermont, before taking a BA in English at Harvard. It was there that his career as a director was launched, albeit in the theatre.

Many years later, on the eve of the award of his Bafta fellowship he told the Guardian that it was there that his passion for social justice was ignited when he saw how audiences reacted to really challenging material. “All I ever wanted to do all the way through was to make a difference,” he would say. After graduating, he directed more than 20 plays in theatres on the US east coast and embarked on his television career after CBS had spotted his talent and commissioned him to direct The Seven Who Were Hanged, based on the novel by Leonid Andreyev.

An anglophile who had visited Britain in order to watch Shakespeare at Stratford-upon-Avon, he was prompted to move there permanently in the early 1960s after seeing a performance of Beyond the Fringe in London on his second night. In 1962 he directed Tennessee Williams’s Period of Adjustment at the Royal Court and in the West End, but his theatre work soon took second place to his documentary career; he became a British citizen in 1995 and was appointed OBE in 2006.

His early TV work in Britain dealt with a variety of topics. The award-winning One of Them Is Brett (1965) was about thalidomide children and demonstrated that, despite their physical disabilities, they were as bright as anyone. In the Name of Allah, about a Muslim community filmed in Fez in Morocco in 1970, was an early indication of his wide scope of interests. His curiosity about institutions led to his explorations of governmental bodies; Inside the Brussels HQ (1975) notably featured Stanley Johnson, then working for the European Commission.

It was his 1982 series, Police, in which he was given access to the Thames Valley force by its chief constable, Peter Imbert, that would perhaps have the greatest lasting effect. In one programme, male detectives were shown interviewing a distressed rape victim in a dismissive manner. “Stop mucking us all about,” she is told by one disgruntled officer. Twelve million people saw the programme: the outrage it provoked led to Margaret Thatcher saying in parliament that “it was not the way to behave”.

Graef said later: “We showed [the film] to the police but they regarded themselves as being nice to her.”

He had already been amazed on a visit to Hendon police training college to hear new recruits being told that 60% of women reporting rape were making it up. Forty years later, that segment from the film still has great resonance. Closing Ranks, his 1988 fiction film about how the police handle accusations of violence, addressed issues that also remain just as relevant today.

While he will be best remembered for his work on criminal justice, his range was wide. His documentary production company, Films of Record, which he set up in 1979, was responsible for Julien Temple’s highly regarded Requiem for Detroit? (2010).

His 2011 BBC Panorama special, The Truth About Adoption, has been credited with the speeding up of adoption processes. Who Cares? (ITV, 2012) exposed the neglect of older people in institutions. Another Panorama special, Kids in Care (2010), and his programmes on Great Ormond Street hospital in London (2010-15) also won plaudits. Murder Blues (2005), which charted the activities of the Met police’s Operation Trident on the issue of black crime, saw him at work on more familiar territory.

He also tackled crime and the law in print, most notably through the books Talking Blues: Police in Their Own Words (1989), Living Dangerously: Young Offenders in Their Own Words (1992) and Why Restorative Justice? (2000). He wrote regularly in the media on the issues.

In a prescient article for the Guardian in 2018 he noted: “Until, and unless, resources are found to restore community policing, to provide legal aid for those caught up in the justice system, and for prison officers to do more than lock people up for most of every day, the criminal justice system is at risk of creating more damage than it prevents.”

He was generous with his knowledge and experience and willing to participate rather than just criticise from outside. This led to his membership of the independent advisory group on race for the Met police and his involvement in leading roles for such diverse organisations as the Institute of Contemporary Arts, Prisoners Abroad and the board of London Transport, for which in 1981 he co-designed the London bus map.

He was a founding board member of Channel 4, a visiting professor of media at Oxford University and chair for more than 20 years of the theatre group Complicité, whose co-founder Annabel Arden said of him: “He was as maverick as we were, he was our rock”.

His energies also extended to the environment, and he worked with Simon Jenkins on a programme that showed that Grade II listed buildings were being destroyed daily in what was meant to be Save Britain’s Heritage Year. “He was utterly bound up in his work and committed to the social purpose of the documentary,” said Jenkins.

With Mike Dibb he made Is This the Way to Save a City? (1974) about plans to redevelop Cardiff. Dibb described him as “like a lawyer - so brilliant at summarising arguments”. Last year he was the first person to attend the exhibition at the Riverside Studios of the paintings of the American prisoner Donny Johnson, the subject of Dibb’s film Painted With My Hair.

He had a lighthearted side and loved music and tennis, and supported Arsenal. Working with John Cleese, he directed three of the films of the Amnesty International benefits, including The Secret Policeman’s Ball (1979). This would happily reunite him with some of the stars of Beyond the Fringe. With Richard Curtis he co-produced the first Comic Relief (1985) and with James Rogan he made Monty Python: The Meaning of Live (2014).

To the very end he was engaged in social justice, tweeting in late February “What a tragic ambition” in response to justice secretary Dominic Raab’s announcement of the creation of 4,000 new prison places in England and Wales and the news that the prison population would soon reach a record high of more than 100,000. He was also still busily engaged on projects right up to a few days before his death. With Rob Beckley, assistant commissioner at the Met police, he was working - “still bubbling with energy,” as Beckley put it - on a three-part radio series on the role of police in society, and with Netflix he had in mind a programme about Portugal’s decriminalisation of drugs.

In 1971 he married Karen Bergemann, and they had a son, Max, and a daughter, Chloe. They divorced in 1983, and three years later he married Susan Richards, the author, Russian expert and co-founder of openDemocracy. She, his children and his brother, John, survive him.

• Roger Arthur Graef, documentary maker and director, born 18 April 1936; died 2 March 2022