The family claimed maternal descent from Sir Robert Stewart, an illegitimate son of King James V of Scotland.

He sailed Garland to the Caribbean Sea in June 1801, bringing Rear-Admiral Robert Montagu to Jamaica,[4] where the ship was wrecked the following year.

[4] In early 1803 he took command of the 38-gun frigate HMS Leda, taking part in several engagements of the Napoleonic Wars.

In 1806 Honyman took Leda on Sir Home Popham's squadron in the occupation of the Cape of Good Hope, and crossed the South Atlantic to take part in the unsuccessful invasion of the Río de la Plata.

[4][8] In the 1780s, Honyman's father Patrick had passed the family estates to Robert's older half-brother William, a successful lawyer whose career had advanced under the patronage of the Tory minister Henry Dundas (later Lord Melville).

[9] Robert was on active service with the navy for nearly all his decade in Parliament, and appears to have never voted or spoken in the House of Commons.