Though nothing is known about his early life, it is likely that as a British wizard, he attended Hogwarts School of Witchcraft and Wizardry when he turned eleven and that he had graduated prior to 1981 as the First Wizarding War ended that year.
During the First Wizarding War, Fenwick became a member of the Order of the Phoenix, an organisation founded and led by Albus Dumbledore, in order to oppose the evil Lord Voldemort and his Death Eaters. Fenwick most likely fought in several battles of the First Wizarding War.
Fenwick was brutally murdered by Death Eaters during the war. One of the Death Eaters fired a curse that blasted Fenwick to pieces, and then disposed of his remains. According to fellow Order member Alastor Moody, the Order, in their search for Fenwick's body, only ever found "bits of him."
- Harry Potter and the Order of the Phoenix (First appearance)
- Harry Potter and the Order of the Phoenix (film) (Possible appearance in Order of the Phoenix photograph)