His sister was the writer and feminist Sophia Dobson Collet (1822–1894).
After abandoning a career in the law due to lack of money, Collet became director of music at South Place Chapel and was heavily involved in the Chartist movement.
This had been known as The Free Press prior to Collet taking it over and was a mouthpiece for the views of David Urquhart.
Collet invited radicals to contribute to the Diplomatic Review and as a result began publishing articles by Karl Marx.
The two became great friends and weekly meetings were held at each other's houses at which Shakespeare readings were given by members of their families.