Knox was born in Brussels,[2] the eldest son in a family connected to the Protestant Irish peerage.
[4] He was educated at a Hampshire private school and attended Trinity College, Cambridge, graduating in 1845.
Encouraged to travel for two years by his concerned father, Knox hoped to see Mexico but was lucky to survive a shipwreck off Yucatán.
The splitting up of the original Oratorian group was partly driven by personal difficulties, and in particular Newman’s attitude to Knox, who was proving troublesome.
In 1867 he defended a maximalist interpretation of the doctrine of Papal infallibility, though in a "dry and moderate tone".