Clennell's father was a hat-manufacturer in Newcastle on Tyne.
Intended for the church, Clennell went into the family firm to support his widowed mother; and then manufactured pins.
He was a contributor to the Commercial and Agricultural Magazine, and attracted many supporters while working on a new journal, assisted by the chemist John Sadler.
[2][3] He wrote for Nicholson's Journal,[4] and was editor of the Tradesman.
[5] He was a contributor to Rees's Cyclopædia, but it is not known on what topics he contributed.