Tyrrell came from a cadet branch of the Essex family which acquired Thornton by marriage in 1526. Tyrrell himself, a younger son, became a lawyer. He took the popular side at the outset of the Civil War, assisting John Hampden to raise forces for Parliament, and later served as colonel under the Earl of Essex. He stood unsuccessfully for Aylesbury at the recruiter election of 1645. Apart from one assessment commission, he held no county office between the execution of Charles I and the collapse of the military junta; nor does he seem to have achieved eminence in his profession. Despite his second marriage to the widow of a Cavalier, he was returned for Aylesbury to Richard Cromwell’s Parliament, and made a commissioner of the great seal by the Rump a few months later.
Tyrrell was returned for the county in 1660. A moderately active Member of the Convention, he made no recorded speeches, but was named to ten committees, including those for giving legal form to the Restoration, considering the indemnity bill, continuing judicial proceedings, confirming parliamentary privileges, and inquiring into the unauthorized printing of parliamentary proceedings. Presumably a supporter of the Restoration, he was unanimously approved as commissioner of the great seal, and raised to the bench before the summer recess. In June 1663 he acquired the freehold of the crown manor of Hanslope, to which Castle Thorpe belonged. He was buried at Castle Thorpe on 16 Mar. 1672, aged 78.