Born in Hollingbourn, Kent County, England, he was the son of Robert and Mary (possibly Sarah ?) (Bowles) Colgate.
His family left England in 1798 and settled in Maryland (citing political reasons for their exodus). In 1804, William came to New York City where he apprenticed as a soap boiler. In 1806 he formed a soap manufacturing company with a partner, a company which would eventually become Colgate-Palmolive.
A devout baptist (baptized in 1808), he donated 10% of his income to Baptist causes, particularly the Hamilton Literary and Theological Institution. After years of involvement (and donated wealth) by himself and two sons (James and Samuel), the school was renamed to Colgate University in his family's honor.
He married Mary Gilbert in 1811.