Clarendon, Frederick Villiers (c.1820–1904), architect and civil engineer, was born in Dublin, one of several sons of Thomas Clarendon (fl. 1800–20), linen draper, of Westmoreland St., and estate developer. Nothing is known of his mother. He entered TCD and graduated BA (1839). Employed (1839–87) by the Board of Public Works, he worked as an assistant (1839) on the construction of the Kenmare suspension bridge, before becoming the first architectural assistant (1841–6) created by the board, and subsequently clerk of works (1846–54). In 1844 he worked as resident engineer on various projects including the Galway docks and the Tralee ship canal, and was subsequently clerk of works for the renovation of the original buildings of Maynooth College, Co. Kildare. He prepared the brief (1847) for the consultants appointed to design the new district asylums for the mentally ill, and collaborated with Jacob Owen (1778–1880) on the design of the asylum in Dundrum (completed 1851).
In 1853 he carried out extensions to the RIA premises in Dawson St.; skilfully creating spatial effects by the use of iron framing devised by Robert Mallet (qv), he designed the museum (later the reading room) and library (subsequently the meeting room), its fine compartmented ceiling inspired by the booking hall at Euston station, London. Promoted to the new post of surveyor of works and buildings (1854–87), he designed (1856–7) the RDS's museum (later renamed the Natural History Museum), Merrion Sq., which was planned to harmonise with Leinster House – then occupied by the RDS – and its Agricultural Hall (1858), a glass and iron structure that was later transferred from Kildare St. to Ballsbridge.
He served as hon. secretary and treasurer (1847–53) to the ICEI and contributed several articles (1846–8) to its Transactions. A member of the RSAI (1853), he was council member (1850–61, 1864–7, 1869–79) of the RIAI, and was elected fellow (1868) and vice-president (1868). On his retirement he devoted himself to charitable work. From about 1881 he lived at 36 Mountjoy Sq., Dublin, where he died 17 October 1904; he was buried in St George's church, Dublin. He married (1853) Margaret Jane Slacke, Jacob Owen's granddaughter; they had two sons and three daughters.