{{Use dmy dates|date=September 2021}} [[File:Guildford JH Mainwaring-Ellerker-Onslow, Vanity Fair, 1875-07-24.jpg|thumb|"The Claimant's Friend". Caricature by "Ape" (Carlo Pellegrini) published in ''Vanity Fair'' in 1875.]] '''Guildford James Hillier Mainwaring-Ellerker-Onslow''' (29 March 1814 – 20 August 1882<ref>{{Rayment-hc|g|2|date=March 2012}}</ref>) was an English Liberal Party politician who sat in the House of Commons from 1858 to 1874.
Guildford Onslow was the second of five sons of Colonel {{abbr|Hon.|The Honourable}} Thomas Cranley Onslow, whose father in turn was a wealthy late-18th-century British royal-family friend and politician, Thomas Onslow, 2nd Earl of Onslow.
His flamboyant name – Guildford – is the county town of the county of Surrey where his family owned land and businesses – was bolstered by the wealth of the father of his mother Susannah, Nathaniel Hillier, who owned the estate of Stoke Park House, Stoke-next-Guildford, Surrey.<ref name=Debrett/> His father started a relatively briefly second-ranking branch of the Earl of Onslow's family, the land owning and land-developing heirs of much of the land of the Earls of Surrey which in 1870 became the senior branch of the family on the accession to the earldom of Guildford Onslow's nephew.
He was educated at Eton College and joined his father's regiment, the Scots Fusilier Guards. He reached the rank of captain and also served in the 11th Regiment of Foot. He was a deputy lieutenant and J.P. for Lincolnshire and the East Riding of Yorkshire.<ref name=Debrett>[https://archive.org/stream/debrettshouseo1870londuoft#page/214/mode/2up Debretts House of Commons and the Judicial Bench 1870]</ref>
In October 1858, Onslow was elected at a by-election as one of the two Members of Parliament (MP) for Guildford in Surrey.<ref name="craig1832-1885">{{cite book |last=Craig |first=F. W. S. |authorlink= F. W. S. Craig |title=British parliamentary election results 1832–1885 |orig-date=1977 |edition= 2nd |year=1989 |publisher= Parliamentary Research Services |location=Chichester |isbn= 0-900178-26-4 |pages=139–140 }}</ref> He was returned at the next three general elections, holding the seat when Guildford's parliamentary representation was reduced to one seat at the 1868 general election, but at the 1874 general election he lost the seat to the Conservative Party candidate, his sixth cousin Denzil Onslow.<ref name="craig1832-1885" />
In 1861 he assumed by Royal Licence the additional surnames of Mainwaring and Ellerker.<ref>{{London Gazette |issue= 2544 |date=3 September 1861 |page=3573 |city=London }}</ref>
Onslow died at the age of 68.
Onslow married a cousin, Rosa Anne Onslow, daughter of General Denzil Onslow of Staughton House, Great Staughton, Huntingdonshire (since 1974 Cambridgeshire).
==References== {{Reflist}}
==External links== *{{hansard-contribs | mr-guildford-onslow | Guildford Onslow}}
{{s-start}} {{s-par|uk}} {{s-bef | before = Ross Donnelly Mangles<br />William Bovill }}
{{s-ttl | title = Member of Parliament for Guildford | years = 1858–1874 | with = William Bovill until 1866 | with2 = Richard Garth 1866–1868 }} {{s-aft | after = Denzil Onslow }} {{s-end}}
{{Authority control}}
{{DEFAULTSORT:Onslow, Guildford}} Category:1814 births Category:1882 deaths Category:Liberal Party (UK) MPs for English constituencies Category:Politics of Guildford Category:UK MPs 1868–1874 Category:People educated at Eton College Category:Deputy lieutenants of Lincolnshire Category:Scots Guards officers Guildford