Later in life du Cros was described by the Revue Franco-Anglaise as dapper, below middle height and of robust build with an expressive face and a high forehead.

Son of Edouard Pierre du Cros who was of French Huguenot descent and Maria Molloy he was educated at The King's Hospital, Dublin.

[5] Two of his sons were beaten in a cycle race by a little-fancied competitor using John Boyd Dunlop's rudimentary pneumatic tyres.

Friends of du Cros, J. M. Gillies and Dublin cycle agent William Bowden, also persuaded John Boyd Dunlop to join them to promote the new company.

[12] He resigned from the House of Commons two years later because of ill health, by the procedural device of accepting the post of Steward of the Chiltern Hundreds.

William Harvey du Cros died at his house Inniscorrig Dalkey county Dublin on 21 December 1918 and was buried in a family vault at Finstock Oxfordshire.

[14][15] Du Cros co-owned the Motor Power Company with S. F. Edge and they imported the French Clement-Gladiator cars, often known as Gladiators, into the UK.