Sydney Kentridge, the protagonist of Thomas Grant’s superb legal saga The Mandela Brief, is that trickiest of biographical subjects: a great man. Grant acknowledges ‘it is rare that, on closer acquaintance, a person touted as a “great” man or woman conforms to the initial description’, but the South African lawyer has been described by countless barristers as the greatest courtroom advocate they had ever seen.

Notable for the apartheid cases he conducted as a defence lawyer of especial distinction and passion, Kentridge has also been admired for his calm and assured bearing in court. The Observer praised him in 1968 as having ‘the face and bearing of an upper-class Regency buck speaking Afrikaans whenever he was obliged to with what sounded like a Knightsbridge accent’. That the advocate was Johannesburg born-and-bred was not considered noteworthy.

Yet this Regency buck was no gilded fop. He was an intense, forbidding presence in or out of the courtroom, and it was said of him in 1977 that ‘it is just as terrifying to be his client as it is to face him on the witness stand’. The clients – who included Nelson and Winnie Mandela, the anti-apartheid lawyer Bram Fischer and the family of the murdered activist Steve Biko – nevertheless remained hugely grateful to him, with Mandela saying: ‘His brilliance shone out, and with it the promise of the career to come.’

Kentridge subsequently had a long and distinguished practice at the British Bar, but The Mandela Brief wisely concentrates on his earlier career in South Africa. Although it is easy to assume that, when he began his advocacy in 1952, he was already dealing with a legal system of hideous bias, it took some time to dismantle what Grant calls the country’s ‘enviable international reputation for the quality of its judges and jurisprudence’, mainly brought about by the 1967 Terrorism Act – a blunt instrument designed to enforce apartheid rules that saw the state plumb new depths of oppressiveness.

Although Kentridge was an advocate, not an activist, there was an inevitable blurring of the lines in the pursuit of justice. As Grant writes: ‘In South Africa during the apartheid years, the practice of law could actually matter… lawyers could not only save lives but could also expose the brutality and malice of the state.’ Kentridge first established his reputation with the so-called ‘Treason Trial’, which stretched from 1956 to 1961 and saw more than 100 people, among them members of the African National Congress, including Mandela, accused of the capital crime of treason.

The case attracted international outrage – the Labour party of the time under Hugh Gaitskell denounced South Africa as no better than a police state – and Grant observes that ‘in its malevolent immensity the Treason Trial seemed like a Kafkaesque version of Jarndyce vs Jarndyce’. Yet Kentridge won, and established his subsequent reputation as a result of his painstakingly brilliant performance in court, which included requesting that the judge should recuse himself, given his clear bias against the defendants – an unsuccessful but morally justified action that confirmed him as a man of integrity as well as courtroom theatrics.

Not, of course, that Kentridge would ever have seen himself as a showman. Unlike his British peers – the George Carmans of this world – he remained someone who concentrated on the facts at hand rather than the opportunity to unleash rhetorical fireworks on the courtroom. Grant writes wryly that ‘an edition of Kentridge’s collected emails would not extend to many pages… he retained his distaste for self-promotion and what he would characterise as the vulgar business of marketing’.

Instead, he concentrated on championing the underdog. The book’s title refers both to the Treason Trial and to the lengthy, exhausting ordeals that Mandela’s wife faced over the course of 16 years. Grant suavely acknowledges that ‘the controversies of her later life have tended to dominate current perceptions of Winnie Mandela’, before writing in heartfelt, precise detail about Kentridge’s unstinting advocacy on behalf of his increasingly desperate client.

This is the second book that Grant, himself a practising barrister, has written about another legendary advocate. The first, 2015’s Jeremy Hutchinson’s Case Histories, was a rollicking account of the defender of everyone from Christine Keeler to Howard Marks, full of humour and human interest. That book was enlivened by the author’s obvious admiration and sympathy for his friend, and so it proves again here.

The tone of The Mandela Brief is darker and angrier, as befits Kentridge’s work. There is a slightly superfluous epilogue dealing with his legal career in Britain, and some readers may tire of Grant’s laudatory (though never hagiographic) treatment of his fellow lawyer. But this is a well-written, deeply researched and wholly gripping book, full of human interest and justifiable passion for the injustice that a determined man spent his life fighting. Would that we had more Sydney Kentridges today.