Samuel Lowry Porter, "Sam" to friends and colleagues, made up for a late start in the law with astonishingly rapid promotion on the Bench, becoming the second Commercial Judge after Robert Wright to bypass the Court of Appeal with promotion straight to the House of Lords. But Porter, less manifestly talented than Wright, had less professional claim to such accelerated career progression, and he appears to have owed his rapid rise to non-judicial considerations.

When Porter's name began to appear in the law reports again during the 1920's, there was a new emphasis on commercial work. He acted in cases involving bills of lading and charterparties, marine insurance, sale of goods, and even salvage. Porter appears to have taken advantage of the post-war surge in commercial litigation to develop a specialist Commercial Court practice, although he continued to take on some more general work, including consumer insurance and insolvency.

Perhaps Porter’s most prominent case at the Bar was In Re Polemis and Furness & Withy [1921] 3 KB 560. Ostensibly a dispute under a time charter, this turned into the leading case on remoteness of damage in negligence. Porter and his leader, R. A. Wright KC, failed to persuade the Court of Appeal that foreseeability of damage formed part of the test of remoteness, although their arguments were vindicated in the 1960's and now represent the law. Porter maintained his emphasis on commercial cases after he was appointed King's Counsel in 1925, though he also added company law and insolvency to his repertoire. He made more than a hundred appearances in Lloyd’s Law Reports in nine years as a KC, though none of his cases had a particularly profound impact on the development of English commercial law. Porter was not a dynamic advocate, though his 'Telegraph' obituarist implied that he was a rather long-winded one. Pale, stooped and slightly built, and fairly short, he had no great physical presence, and he adopted a style which was affable but very quiet. The Times reported that, when he was a Judge, it was often difficult to hear what he was saying in Court. But he was tenacious, could put a question or an argument forcefully when the ocassion demanded, and had a physical robustness which belied his delicate frame and enabled him to meet the demands of the long working hours of a busy and successful KC.

Porter reinforced his reputation as a commercial specialist by becoming senior editor of 'Scrutton On Charterparties' when T.E. Scrutton abandoned his own work after the Hague Rules, to which he indignantly objected, were made part of English law. Porter also strengthened his professional credentials by serving as a Recorder in Newcastle-under-Lyme and then Walsall. Part-time judicial office as a Recorder was often a springboard to a career on the permanent Bench. Porter's opportunity came in 1934, when Adair Roche's promotion to the Court of Appeal and Edward Acton's retirement created two King's Bench vacancies. Roche and Acton, both Commercial Judges, were replaced on the same day by two new Judges who would also sit in that Court, Porter and John Edward Singleton. Porter’s appointment did not create any great surprise, although it did not generate much enthusiasm either. The Law Times was prepared to go no further than to say that it was "generally acceptable".

With accusations of suspicious share-trading also emerging, Parliament established an inquiry, and Porter was appointed to head it. Working quickly, the Budget Inquiry heard evidence in mid-May, sitting in the Royal Courts of Justice with Porter dressed in his judicial robes, and reported in early June. It concluded that J.H. Thomas had disclosed Budget details in advance to friends and associates, including fellow MP Sir Alfred Butt (a Conservative), who had used the information for financial gain. The disgraced Thomas grumbled about the inquiry's procedure, but resigned from the Commons. Butt denied wrongdoing, and initially seemed determined to brazen it out, but he ultimately followed Thomas's example. The inquiry cleared Leslie Thomas, concluding that he had known nothing about the leaks, but he still lost his job in the City. He later became a Conservative MP.

Nothing which Porter did in the King's Bench matched the public impact of the Budget Inquiry. Virtually all of his reported decisions were commercial, although he also sat in the Court of Criminal Appeal and went Circuit. Porter was of the school of thought that a first instance Judge's job was to decide each case on its facts. He exhibited little inclination to refine or restate the law, and he produced concise judgments which said no more than necessary. Indeed, The Times thought that some of his judgments were too short, and that they showed signs of being stitched together from his notes and extracts from key documents, rather than being carefully written from scratch. But this is a phenomenon familiar to modern Commercial Court practitioners, and it invariably reflects a commendable judicial concern to deliver a decision as quickly as possible: the more polished a judgment, the longer it takes to write, and the more the parties are kept waiting. The Law Times thought that Porter’s usual environment was partly to blame, commenting that “the Commercial Court, demanding a constant study of the correspondence and documents of businessmen, often loosely and obscurely worded, is not the best school of literary expression”. Even making all allowances, however, none of Porter's Commercial Court judgments were particularly memorable. His most striking decision was a refusal to follow a settled custom, which had been established by T.E. Scrutton in 1911, of transferring into the Commercial Court any action set for trial in London before a special jury. Scrutton had probably assumed that any London special jury case would be commercial, but this was not always so. When a slander action was set down for special jury trial in 1937, Porter flatly refused to let it into the Commercial Court, and the Court of Appeal upheld his decision.

Porter sometimes exhibited an independent streak in the Lords. For example in Joyce v DPP [1946] AC 347, he, alone of the Law Lords, he held that Lord Haw-Haw's conviction for high treason was unsafe because the prosecution had not discharged the burden of proof. In the more familiar field of commercial law, Porter gave leading judgments in Smith, Hogg v Black Sea & Baltic [1940] AC 997, in which the Lords held that a shipowner was fully liable for loss caused by unseaworthiness notwithstanding that an excepted peril was a concurrent cause; Yorkshire Dale v Minister of War Transport [1942] AC 691, a landmark case on the test for causation in insurance claims (and more generally); and Tankexpress v Compagnie Fianciere Belge [1949] AC 76, which established that even an innocent delay in payment could trigger an owner's right to terminate a time charter under a withdrawal clause. Porter was also on the panels which decided Joseph Constantine v Imperial Smelting [1942] AC 154, which resolved who bears the burden of proof on self-induced frustration, and the puzzling The 'Greystoke Castle' [1947] AC 265, which appeared to imply that a plaintiff could recover pure economic loss if the defendant's negligence had created a risk of damage to the plaintiff's property, even if no actual damage had occurred.

Unmarried, Porter moved into his old Cambridge College when he was bombed out of his flat during the Second World War. He had planned this as a temporary arrangement, but he felt so at home that he settled down for the duration of hostilities, catching the morning train to London for appeal hearings. While back at Emmanuel, Porter nurtured the College's Law Society and gave generously of his time to advise students about a career at the Bar. Porter was often unwell in his later years in the Lords. He retired for health reasons in 1954, although he was well enough to retain his position as the judicial member of a panel for the conciliation of coal industry disputes, and to sit on about a dozen House of Lords appeals in retirement. His last judgment was handed down only a week before his death in a London nursing home in February 1956, although Porter was by then too unwell to deliver his decision in the Chamber of the House in the customary fashion. Showing that he retained his independent-mindedness, Porter decided that the plaintiff ought to have looked where he was going, and dissented from the majority view that the shipowners should have erected a safety barrier. Porter's retirement co-incided with a shake-up of the government, and he was replaced as Law Lord by Lord Simonds, who returned for a second stint as a Lord of Appeal after a three-year sabbatical in Winston Churchill's Cabinet as Lord Chancellor. Like Porter, Simonds had been promoted direct from the High Court when he first went to the Lords. As Gavin Simonds KC, he had been a member of Porter's Budget Inquiry in 1936.

Porter had been a good tennis player when he was young, playing for his university. In later life, his main interest away from the courtroom appears to have lain in the International Law Association. He was President in 1946, when the Association held its first meeting since before the War: to Porter’s delight, it was held in Cambridge. He was also sociable (he was a member of three London clubs), and was fond of his Inn, as well as of his old College. He had been due to serve as Treasurer of the Inner Temple in 1957. Porter may not have been an outstanding Judge, but he was clearly enormously endearing, and he was much liked. The day after his death was announced, tributes were paid at the start of judicial business in the House of Lords, the Privy Council, and in the Commercial Court, where Frederic Sellers was sitting. Sellers reminisced about Porter’s good humour when he had been at the Bar, while future Commercial Judge Eustace Roskill KC, who, as a young barrister, had shadowed Porter when he was a new Judge, spoke of his kindness. Lord Simonds conceded that the King's Bench and the Lords had seen cleverer men and better lawyers, but insisted that "there never was a Judge of whose absolute fairness and determination to do justice according to law counsel or litigant could be less in doubt". The funeral service was held in the chapel of Emmanuel College.