William Lindsay Alexander (24 August 1808 – 20 December 1884) was a Scottish church leader.
He was born at Leith, and was educated at the universities of St Andrews and Edinburgh, where he gained a lasting reputation for classical scholarship. He entered Glasgow Theological Academy under Ralph Wardlaw in September 1827, but in December of the same year he left to become classical tutor at the Blackburn Theological Academy, afterwards the Lancashire Independent College, in north-west England. He stayed at Blackburn until 1831, lecturing on biblical literature, metaphysics, Greek and Latin.
After short visits to Germany and London, he was invited back to Edinburgh in November 1834 to become minister of North College Street church (afterwards Argyle Square), an independent church which had arisen in 1802 out of the evangelical movement associated with the Haldane brothers, Robert and James. When the church sold its property to the government to make way for the National Museum of Scotland, Alexander's congregation worshipped in the Queen Street Hall until 1861 when the new church was completed on George IV Bridge, renamed Augustine Church because of Alexander's strong, albeit independent Augustinian influence in his sermons. He deliberately put aside the ambition to become a pulpit orator in favour of the practice of biblical exposition, which he invested with charm and impressiveness. In 1836 he became one of the editors of the Congregational Magazine, to which he contributed articles on biblical literature and theology and on the "voluntary" controversy. In 1840 he delivered the Congregational Lecture in London on the "Connection and Harmony of the Old and New Testaments."
Alexander took an active part in the "voluntary" controversy which ended in the Disruption of 1843, but he also maintained broad and catholic views of the spiritual relations between different sections of the Christian church. In 1845 he visited Switzerland with the special object of inquiring into the religious life of the churches there. He published an account of his journey in a book, Switzerland and the Swiss Churches, which led to an interchange of correspondence between the Swiss and Scottish churches. In 1845 he received the degree of Doctor of Divinity (D.D.) from the university of St Andrews.
In 1861 he undertook the editorship of the third edition of John Kitto's Biblical Encyclopaedia, with the understanding that the whole work should be thoroughly revised and brought up to date. In January 1870 he became one of the committee of Old Testament revisers, and by his thorough biblical scholarship rendered exceptional service to the board; he enjoyed the work and devoted much time to it for the next fourteen years. In 1877 he became principal of the Edinburgh Theological Hall, a position which he held until his death, in spite of many alternative offers.