After the execution of the unfortunate Queen of Scots, he devoted himself to what was termed the Spanish faction, and endeavoured carry out the schemes of a party, who, distrusting the vague promises of James, were anxious to secure the succession to a Catholic,--the Infanta of Spain, or the Duke of Parma.

On the insurrection of the Earl of Essex, he took part with that ill-fated nobleman; and, though he escaped condign punishment for the offence, he was imprisoned and heavily fined.
From this time his career ran in darker channels.

"Hunger-starved for innovation," as he is finely described by Camden,--imbued with the fiercest religious fanaticism,--eloquent, wily, resolute,--able alike to delude the powerful and intimidate the weak,--he possessed all the ingredients of a conspirator.

Associating with men like himself, of desperate character and broken fortunes, he was ever on the look out for some means of retrieving his own condition, and redressing the wrongs of his church.

Well informed of the actual state of James's sentiments, when, on that monarch's accession, confident hopes were entertained by the Romanists of greater toleration for their religion, Catesby was the first to point out their mistake, and to foretel the season of terrible persecution that was at hand.