The first Commercial Judge to be portrayed on the New York stage by a retired Anglican archbishop, Johan Van Zyl made significant physical and intellectual journeys during his life. After establishing himself as one of South Africa's leading advocates, he left his homeland just as he was approaching the peak of his career to start all over again in England. And, having made his reputation as a commercial jurist, he became best known for public remarks of a political nature, most prominently in a series of outspoken attacks on the foreign and domestic policies of the New Labour government.

Although born into apartheid South Africa's elite, Steyn became disenchanted with the system of segregation and discrimination which his fellow-Afrikaners had created. This process was relatively gradual. During the 1960's, he was perceived as a sufficiently sound establishment figure to receive regular police instructions, and he represented the state security services at a high-profile law and order inquiry in 1963. By the early 1970's, however, he was acting for students who had been attacked by the police on the steps of Cape Town cathedral during an anti-apartheid protest. Although increasingly disaffected, Steyn did not become a vocal critic of white rule while he lived in South Africa. The explanation which he gave to surprised colleagues when he emigrated to England in 1973 was simply that he thought that the opportunities for commercial work were greater in London. He was called to the Bar by Lincoln's Inn, and joined the commercial set at 4 Essex Court as a pupil.

Beginning again at the bottom aged forty-two and after more than fifteen years in practice would have been daunting under the best of circumstances. Two factors aggravated the challenge for Steyn. First, his pupil master was the perfectionist Anthony Colman. Colman, who was six years younger than his pupil, reputedly recommended significant revisions to every piece of work which Steyn produced. Second, the thick accent which was part of Steyn's heritage (he grew up speaking Afrikaans as his first language) made him work hard to be understood in his early Court appearances, and he acquired a reputation as a ponderous advocate. But he was also calm and methodical, and ran a well-ordered and carefully-prepared case. Although only a handful of his appearances at the junior Bar in England found their way into the law reports, he made sufficient impression to become Queen's Counsel in 1979.

Steyn achieved an altogether greater prominence as a QC. In particular, he argued four leading shipping cases in the House of Lords within two years. Unhappily, he had the misfortune on each occasion to come up against the unmoveable object of an unsympathetic Kenneth Diplock. In The 'Scaptrade' [1983] 2 AC 694, Steyn strove to persuade the Lords that the equitable doctrine of relief against forfeiture applied to a time charter withdrawal clause. Delivering the only speech, Diplock explained that the Lords had only given Steyn permission to appeal so that that they could make clear just how ridiculous they thought his argument was. At least Diplock was (uncharacteristically, at this late stage of his career) complimentary about Steyn's presentation of his case. In The 'Miramar' [1984] AC 676, which remains the leading case on the incorporation of charterparty clauses into bills of lading, Diplock again said that the Lords had always known that Steyn was wrong. This time, they had granted him permission to appeal so that they could explain why "no business man who had not taken leave of his senses" would construe the contract in the way which he suggested. Diplock was even more brusque in The 'Hollandia' [1983] AC 565, which established the scope of the overriding effect of the Hague-Visby Rules when they apply by statute. Steyn had barely finished opening the appeal before Diplock interrupted to announce that he had lost. In The 'Evia' (No 2) [1983] 1 AC 736, in which the Lords explored and explained the nature of a charterer's safe port undertaking, Diplock left the leading speech to the unfailingly polite Eustace Roskill, who was at least prepared to accept that Steyn might have some sort of colourable case. But the outcome was another defeat.

Among the commercial cases, his judgment in Singer v Tees & Hartlepool [1988] 2 Lloyd's Rep 164 was significant in the development of the modern doctrine of bailment on terms, and was later endorsed by the Privy Council in The 'Pioneer Container' [1994] 2 AC 324. In Associated Bank v Credit du Nord [1989] 1 WLR 255, Steyn held that a guarantee of a leaseback of machinery which turned out not to exist (the lessee was a fraudster) was void for common mistake. It was an eye-catching decision, given that, historically, common mistake defences had seldom succeeded. Steyn gave important judgments on the nature of an owners' lien on subfreights in The 'Cebu' (No 2) [1993] QB 1 and on the conclusion of contracts by exchange of written messages in The 'Junior K' [1988] 2 Lloyd's Rep 583. Patient and courteous during hearings, but decisive and clear when it came to making decisions, Steyn was highly-regarded. When he was promoted to the Court of Appeal in 1992, he bypassed David Hirst, John Hobhouse, Anthony Evans and Mark Saville, who had all become Commercial Judges before him (although they all followed him up the judicial ladder within the following few months). 

Prominent among Steyn's commercial appeals were Continental Bank v Aeakos [1994] 1 WLR 588, which was significant in the development of the anti-suit injunction jurisdiction, and First Energy v HIB [1993] 2 Lloyd's Rep 194, in which Steyn found a way around the problematic decision of the House of Lords in The 'Ocean Frost' [1986] 1 AC 717, which had appeared to severely restrict the scope of vicarious liability for misrepresentation. As a Lord Justice, Steyn also dealt with competition, defamation, insolvency, land law, landlord and tenant, and tax cases, as well as a lot more crime. But his time in the Court of Appeal was brief. After only three years, he was made a Lord of Appeal in Ordinary.

Steyn spent just over a decade as a full-time Law Lord, and sat on the occasional appeal for two more of years after his formal retirement. He participated in more than five hundred House of Lords and Privy Council appeals, on topics ranging from the tax status of chocolate-covered teacakes under European law to the mens rea of the offence of money laundering, and from the constitutions of the Bahamas and Mauritius to liability for deep vein thrombosis contracted during international flights. They included some important commercial cases. Relieved classification societies worldwide welcomed Steyn's leading judgment in The 'Nicholas H' [1996] AC 211, in which he held that societies who carelessly gave a seal of approval to unseaworthy ships did not owe a duty of care to cargo owners. In The 'Rafaella S' [2005] AC 243, he held that the Hague/Hague-Visby Rules applied to straight bills of lading, resolving a long-standing debate. In The 'Jordan II' [2005] 1 WLR 136 on the other hand, he declined to resolve another controversy about the Rules. Five decades before, the Lords had decided in Renton v Palmyra [1957] AC 149 that the Rules permitted the parties to allocate responsibility for cargo operations. Shipping lawyers had argued ever since about whether or not the decision was right, but Steyn declined to say, deciding that Renton should be followed, not because it was necessarily correct, but simply because it had stood for a long time. In The 'Giannis NK' [1998] AC 605, he explored the nature of a shipper's liability for dangerous cargo, and in In Lesotho v Highlands [2006] 1 AC 221, he expounded on the somewhat elusive distinction between arbitrators exceeding their powers and merely mistaking the extent of their powers.

Steyn's broadsides were heartfelt. But the rather dogmatic manner in which he tended to express himself suggested that he harboured a starkly binary perception of right and wrong which admitted of no room for argument. He was, thought The 'Times', "a man of forthright opinion who was untroubled by self-doubt", and he sometimes conveyed the impression that anyone who disagreed with him was necessarily wicked, or stupid, or both. Steyn's strong personal sense of moral rectitude sometimes affected his judicial work, for example in death row cases in the Privy Council: an opponent of capital punishment, he had a reputation for inventing devious ways to allow appeals. His tactlessness occasionally created professional complications too. He used one of his lectures to condemn the government for derogating from the Human Rights Act in implementing new terrorism legislation. When the legality of that derogation was appealed to the Lords, Home Secretary David Blunkett and Attorney-General Peter Goldsmith made representations to Senior Law Lord Tom Bingham that Steyn should not participate. Objectively, it was hard to deny that they had a point, and Steyn was not one of the seven Lords who heard A v Secretary of State [2005] 2 AC 68. But he grumbled about the suggestion that anyone might think that he had pre-judged the issues just because he had ventilated his opinions in public, and he harboured a lasting resentment.

A number of Steyn's more colourful public pronouncements about the Gulf War were incorporated into a play, with Steyn appearing as a character reading out lines from some of his lectures. The work was staged in London and in New York, where, in one 2004 performance, Steyn was portrayed by fellow South African Desmond Tutu, the former Archbishop of Cape Town.

Publicly a rather austere character (although alleged to be capable of dry wit in private), Steyn was little given to relaxing pastimes. Most of his activities away from the Bench involved various legal education and development organisations, and he sat on numerous committees. But he did enjoy a game of tennis, and it was on the tennis court that he met his second wife, Susan Lewis. He became stepfather to her son and daughter when they were married.

Johan Steyn died from a brain haemorrhage in November 2017. His younger daughter, Karen, was appointed a Judge of the Queen's Bench Division in 2019.