Porter, William (1805–80), attorney general of the Cape Colony, was the second son of the Rev. William Porter (qv), presbyterian minister of Limavady, Co. Londonderry, and his first wife Mary (née Scott), both of them the offspring of tenant farmers near Omagh, Co. Tyrone. The Rev. William Porter was a leading protagonist in the heterodox or New Light party within the church, and when his group seceded in 1831 he became the first moderator of the unitarian remonstrant synod. Porter was educated at the Artillery Lane school in Londonderry and then apprenticed to John Classon, a prosperous iron and timber merchant in Dublin, the brother of the Rev. William Porter's second wife, Eliza. The Classons, like Porter's father, adhered to the New Light party and supported the liberal causes championed by the Northern Whig, Belfast's liberal newspaper, which was owned and edited by Frank Dalzell Finlay (qv), the husband of William Porter's sister, Mary Ann. His elder brother, John Scott Porter (qv), who like their father and two half-brothers was a unitarian minister, was a lifelong friend of the radical Joseph Chamberlain's father. William Porter on more than one occasion declared himself to be a liberal born and bred.
Porter showed no aptitude for business; his interests were literary and historical and he was an eloquent public speaker. So the Classons proposed that he should turn to law and John Classon undertook to support him while he kept his terms. The plan was adopted and Porter was called to the Irish bar in 1831. During the eight years he practised on the north-east circuit he took no active part in Irish politics, though his close associates at the bar were leading liberals and his views on the issues of the day were those propagated by his brother-in-law's paper. When Daniel O'Connell's (qv) accord with Lord Melbourne's (qv) whig government opened hitherto unattainable legal appointments to catholic and non-conformist lawyers, Porter was appointed in 1839 attorney general of the Cape Colony.
The Cape was a racially complex colony, Dutch until 1815 and until recently slave-owning, and still in process of being integrated into the British empire. Porter's was primarily a legal post, but as legal adviser to the governor and a member of the executive and legislative councils he was involved in political issues also. The nature of his office and the evolutionary state of the colony positioned him to influence developments; his professional ability and personal magnetism inspired confidence in the colony; and the high regard in which he was held by the colonial office in London resulted in his becoming the most influential public figure of his day at the Cape.
In the legal sphere Porter worked consistently for absolute equality before the law for all, regardless of class or race, and he was sufficiently satisfied with the scope his office afforded for promoting that end to decline offers of promotion to the bench. The same principle of equality of treatment was basic to the constitution he drafted when representative government was established in the colony. By fixing a low property qualification and giving the franchise to all men regardless of race he excluded, as he said, nothing but vagrancy and crime.
As an ex-officio member of the new parliament, and after retiring from the attorney generalship in 1865 as an elected member of the house of assembly, he contributed greatly by precept and example to the smooth functioning of the institution. When eventually responsible government was conceded the governor called on him to draw up the constitutional amendment, and when it was passed the governor pressed him to become the first prime minister. He declined, as he had declined offers of advancement and honours throughout his career. When the Cape parliament voted him full salary on his retirement instead of the normal pension, he directed that the difference between the two should be paid to the board of examiners, the forerunner of the University of the Cape of Good Hope.
The first session under the new constitution was Porter's last. His friend Hugh Lynar, who had come to the Cape with him in 1839 and had lived with him ever since, died in 1873 and Porter returned to Belfast where he lived with his brother John Scott for the last seven years of his life. He died on 13 July 1880 and was buried in Belfast borough cemetery. The charitable generosity which characterised him all his life was evident in the provisions of his will. After bequests to several Cape Town charities and to every public library in the colony, he donated £20,000 for the establishment of a reformatory for boys. If parliament decided against a reformatory, he directed that part of the bequest should be used to promote the education of women at university level.