Howe was born in , the son of an Anglican priest. He left Trinidad for London aged 18 to enter the legal profession at Middle Temple, but he swapped the law for journalism. He returned to Trinidad, where his uncle and mentor, radical intellectual CLR James, inspired Howe to combine writing with political activism. A brief spell as assistant editor on the Trinidad trade union paper The Vanguard was followed by return to Britain as editor of British magazine Race Today.
He became a member of the British Black Panther Movement, and in August 1970, following a protest, Howe was arrested and tried for riot, affray and assault. He was acquitted after a trial at the Old Bailey. Later, he was the editor of the magazine Race Today and was imprisoned for three months for assaulting a police officer. The celebration following his release was recalled in the song Man Free by poetLinton Kwesi Johnson. The central lines of the song describe Howe’s legal fight: “I stand up in the court like a mighty lion, I stand up in the court like man of iron, Darcus out of jail, Shabba!”.
Howe organised the 20,000 strong Black People’s March 1981 claiming official neglect and inefficient policing of the investigation of New Cross Fire in which 13 black teenagers died.