William Fraser was born in the Mearns, Kincardineshire, on 18 February 1816. After private education in Stonehaven, in 1830 he began a five-year apprenticeship with the firm of Messrs., Brand and Burnett, solicitors in the town. In 1835 he went to Edinburgh where he joined the firm of Hill and Tod, WS, and continued his education at Edinburgh University , studying Scots' Law and conveyancing. He also took classes in French.

Many of the legal cases in which he became involved had required antiquarian and, in particular, genealogical research, and he was therefore introduced at an early stage to those studies in which he later on would became an expert. He steadily built up a great body of knowledge which made possible his great series of fifty or so volumes on the histories of between twenty and thirty of the leading noble and landed families of Scotland - the Stirlings of Keir, 1858; the Montgomeries, 1859; the Maxwells of Pollok, 1863; the Carnegies, 1867; Grandtully, 1868; Colquhoun, 1869; Carlaverock, 1873; Lennox, 1874; Cromartie, 1876; Scotts of Buccleuch, 1878; Menteith, 1880; Grant, 1883; Douglas, 1885; Wemyss, 1888; Haddington, 1889; Melvilles, 1890; Sutherland, 1892; and Annandale, 1894.

Fraser was Keeper of her Majesty Queen Victoria's Records in Scotland, from 1852-1894. In 1882 the University of Edinburgh conferred on him the honorary degree of LL.D. In 1885 he was created a Companion of the Order of the Bath and in 1887 he was made a Civil Knight Commander of the Bath, being invested by Queen Victoria at Osborne House on 2 August 1887.

Sir William Fraser, KCB, LL.D., solicitor, notable expert in ancient Scottish history, palaeography, and genealogy, died on 13 March 1898. The Sir William Fraser Chair of Scottish History and Palaeography at the University of Edinburgh, was founded in 1901.

The work Facsimiles of Scottish Charters and Letters prepared by Sir William Fraser, K.C.B., LL.D. for his series of Scottish family histories was published and printed by Oliver and Boyd, 1903.