William Slater was born in Northamptonshire, England in 1818 [or 1819 - sources differ]. He was articled to Richard Cromwell Carpenter (1812-1855) in London and subsequently worked with him as his assistant. After leaving Carpenter's employ, Slater established his own independent practice in London and for a period was assisted by William Bassett-Smith (1830-1901) who had been a pupil of Carpenter. Following Carpenter's death in 1855 Slater took over his practice. From 1863 to 1872 he was in partnership with Carpenter's son, Richard Herbert Carpenter (1851-1893) as Slater & Carpenter.
Slater was elected an Associate of the Royal Institute of British Architects (ARIBA) in 1855 and a Fellow of the Royal Institute of British Architects (FRIBA) in 1859. He died at 54 Myddleton Square, Pentonville, London on 17 December 1872
Slater's practice was mainly engaged in the restoration of churches. His most significant work was Loughborough Town Hall in Loughborough, Leicestershire, designed in the Italianate style and completed in 1855.
See: Historic England; British Listed Buildings; and Wikipedia [link below]
Directory of British Architects 1834-1914. Compiled by Antonia Brodie, et al. Volume 2: L-Z. London; New York: British Architectural Library, Royal Institute of British Architects/Continuum, 2001
Eastlake, Charles L. A History of the Gothic Revival. London: Longmans, Green & Co., 1872
Elliott, John. ‘Lancing College Chapel: A Question of Attribution’. Architectural History vol. 39, 1896 pp. 114-123
‘Obituary’. The Builder vol. 30, 21 December 1872 p. 1002
‘Obituary’. The Builder vol. 31, 1 February 1873 p. 83
‘Obituary’. Proceedings of the Royal Institute of British Architects 1873-74 pp.214-215