He was educated at the Edinburgh Academy where he was a senior Ephor (prefect).
[1] For his National Service, he was commissioned into the Argyll and Sutherland Highlanders and served in British Guyana.
[1] Prosser became an advocate in 1962, and served as Standing Junior Counsel in Scotland for the Board of Inland Revenue (1969–1974.
[1][3] Prosser's legal work also included serving on the Scottish Committee of the Council on Tribunals,[2] as trustee (2002–2007) for the Franco-British Council, and as President of the Franco-British Lawyers’ Society.
[1] He was also chairman of the Royal Fine Art Commission for Scotland (1990–1995), the Royal Lyceum Theatre (chairman, '87-92), the Scottish Architectural Education Trust (1994–2007), and the Sir Walter Scott Club (1993–1996).