His grandfather was an independent minister at Wolverhampton, and afterwards assistant to James Wheatley at the Norwich Calvinistic Methodist tabernacle.
His father, Jacob Brettell, became a Calvinistic preacher at the age of seventeen, and after serving various chapels became an independent minister at Sutton-in-Ashfield in 1788.
He became Unitarian minister at Cockey Moor (now called Ainsworth), Lancashire, in July 1814, and removed to Rotherham in September 1816.
He was a strong liberal, and took an active part in the anti-corn-law agitation, being an intimate friend of Ebenezer Elliott (1781–1849), the corn-law rhymester.
His eldest son, Jacob Charles Cates Brettell, born 6 March 1817, was partly educated for the Unitarian ministry at York, became a Roman Catholic, and went to America, where he was successively classical tutor at New York, minister of a German church, and successful member of the American bar in Virginia and Texas; he died at Owensville, Texas, 17 January 1867.