The son of an Aberdeen merchant, he began work as a coppersmith and won a government contract to sheath ships' hulls in copper.

At the time he was the greatest landowner in the county, with some of the largest collected lands in Scotland.He was not popular with local people, but nevertheless his family retained great influence over the area for two centuries.

As a successful coppersmith from Aberdeen, among other products, he manufactured sugar boiling pans and rum stills for export to Jamaica.

Although William preferred the newest fashion (and purchased the best furniture and household goods from makers in London and Edinburgh) he did not spend money recklessly, ordering the new servants' wing to be furnished 'in the cheapest way'.

The Forbes household settled down after William's marriage and he began to spend more time in Callendar House and give his brother David greater control of the business in London.