Sir James Thomas Knowles KCVO (1831 – 13 February 1908) was an English architect and editor.
James Knowles was born in London, the son of architect James Thomas Knowles (1806–1884) and himself trained in architecture at University College and in Italy. He designed, amongst other buildings, three churches in Clapham, Lord Tennyson's house at Aldworth, the Thatched House Club, the Leicester Square garden (as restored at the expense of Baron Albert Grant), and Albert Mansions, Victoria Street, Westminster. However, his preferences led him simultaneously into a literary career. In 1860 he published The Story of King Arthur. In 1866 he was introduced to Alfred Lord Tennyson and later agreed to design his new house, Aldworth, on condition there was no fee; this led to a close friendship, Knowles assisting Tennyson in business matters and, among other things, helping to design scenery for The Cup when Henry Irving produced that play in 1880.
Among his commissions were Mark Masons' Hall, London, three churches in Clapham, South London: St Stephen, St Saviour's and St Philip's, the Albert Mansions at Victoria Street and in 1882 enlargement of the Royal Sea Bathing Hospital at Margate in Kent. Knowles was also responsible for the layout of Leicester Square as a public space.
Knowles corresponded with a number of the most interesting men of the day, and in 1869, with Tennyson's cooperation, he founded the Metaphysical Society, the object of which was to attempt some intellectual rapprochement between religion and science by getting the leading representatives of faith and unfaith to meet and exchange views. Members included Tennyson, Gladstone, W. K. Clifford, W. G. Ward, John Morley, Cardinal Manning, Archbishop Thomson, T. H. Huxley, Arthur Balfour, Leslie Stephen, and Sir William Gull. The society formed the nucleus of the distinguished list of contributors who supported Knowles in his capacity as an editor.