He is remembered for his involvement in a plan to kidnap King James I of England, made together with another Catholic priest William Watson in the Bye Plot.
Clark took an active part in the Archpriest Controversy: he was one of the "appellants", the 33 priests who signed the appeal against George Blackwell dated from Wisbech Castle, 17 November 1600.
An attempt was made to give to the first clause of the breve of Pope Clement VIII, in favour of the appellants (5 October 1602), the appearance of restoring to them the canonical faculties which had been recently withdrawn.
On being apprehended Clark was committed to the Gatehouse Prison at Westminster, and then moved to the Tower of London.
Sir Dudley Carleton, who was present, wrote: "The two priests that led the way to the execution were very bloodily handled".