Born, in Jamaica, his family returned to England in 1770 to settle at Prinknash Park near Gloucester. Howell studied at Christ Church, Oxford but did not graduate, instead moving on to Lincoln's Inn and being called to the bar in 1790.

In 1808, William Cobbett asked Howell to edit a new edition of the State Trials, a work aspiring to aggregate all the important cases on public law in England. Howell worked on the project from 1809 to 1814, his son, Thomas Jones Howell taking over from him. A modern edition of the State Trials was edited by Donald Thomas and published from 1972 onwards.