'As much as people admire her, they don't know the half of it.' This observation, made by journalist and biographer Irin Carmon at the start of Julie Cohen and Betsy West's exhilarating documentary about US Supreme Court Justice Ruth Bader Ginsburg, will prove resoundingly true by its end. With unprecedented access to its subject's life and work, bolstered by a raft of talking heads from those who know her personally and professionally, it's a lively celebration of a woman who can legitimately claim to have changed the world.

Taking a traditional chronological approach, it explores how Ginsburg journeyed from Harvard in the 1950s to becoming one of the most influential lawyers in United States history, specialising in gender discrimination. She is also one of only four women ever to serve on the Supreme Court, on which she has sat since 1993. It's a remarkable career, and that Ginsburg was married and the mother of a 14-month-old daughter when she started at Harvard, and nursed both her late husband and herself through cancer bouts, is testament to her unshakeable grit and graft.

Indeed, Ginsburg's friends and family speak reverentially about her work ethic, while also affectionately describing her sombre persona. Colleagues tell of a quiet woman with no talent for small talk, but an innate ability to present a courtroom argument so dynamically that it has often resulted in a change to the law. Ginsburg herself lends anecdotes and memories, and more candid on-screen moments – her laughter as she watches a Saturday Night Live sketch about herself, for example – are particular highlights.

There can be no doubt that Ginsburg has helped affect real change – from challenging traditional 1950s notions of women as subservient homemakers, to fighting cases about equal pay and abortion rights. But there is still so much more left to do, particularly at a time when rampant Trumpism has turned Ginsburg from liberal campaigner to dissenting voice.

Yet, just as there's something hugely comforting about Ginsburg herself, the tireless octogenarian who has inspired numerous generations and become a pop culture icon in her own right, there's also something intensely hopeful about RBG. While far-right voices may be increasing in volume, it's a timely reminder that there are always those prepared to stand up and fight for human rights, no matter how long and exhausting the battle.

Limited release from Fri 4 Jan.