Born in Northern Ireland, Grosvenor moved from an island in the middle of Lower Lough Erne to be educated at Sunningdale and Harrow boarding schools in the south of England.

Via Grosvenor Estates, the business he inherited along with the dukedom in 1979, the Duke was the richest property developer in the United Kingdom and one of the country's largest landowners, with property in Edinburgh, Liverpool, Oxford, Cambridge, Southampton and Cheshire, including the family's country seat of Eaton Hall, as well as 300 acres (120 ha) of Mayfair and Belgravia in Central London.

During the second half of the 20th century, the business expanded into the Americas and developed Annacis Island and Vancouver, both in British Columbia in the west of Canada in the 1950s.

[5] As a child, the Duke lived on an island in the middle of Lower Lough Erne in Northern Ireland (Ely Lodge, Blaney, County Fermanagh).

[9] After entering RMA Sandhurst in 1973, he passed out as an officer cadet and was commissioned a second lieutenant in the Territorial and Army Volunteer Reserve of the Royal Armoured Corps (Queen's Own Yeomanry) on 13 May 1973.

[19][20] He was also appointed Colonel-in-Chief of the Canadian Royal Westminster Regiment, the North Irish Horse, and as Colonel Commandant Yeomanry.

[21] In 2004, he was appointed to the new post of Assistant Chief of the Defence Staff (Reserves and Cadets), with promotion in the rank of major-general.

In March 2007, having served in the Ministry of Defence as Assistant CDS for four years, he handed over responsibility for 50,000 reservists and 138,000 cadets to Major General Simon Lalor, in the wake of the Eliot Spitzer prostitution scandal in which Westminster was also implicated.

[5] In 2011, having already funded a feasibility study, the Duke purchased the estate at Stanford Hall, Nottinghamshire, to make possible the creation of a Defence and National Rehabilitation Centre (DNRC) to provide the highest quality support for military casualties.

Despite his poor educational attainments, Westminster was given several honorary degrees and fellowships (listed below) in later life and took an outward-looking interest in youth.

He was a member of the MCC and Royal Yacht Squadron and President of Worcestershire County Cricket Club in 1984–1986 and of the Youth Sports Trust 1996–2004.

Their children are: In 1998, the Duke suffered a nervous breakdown and had depression, citing the overwhelming pressures of business and public life.