 Cornwallis was appointed High Sheriff of Norfolk and Suffolk for 1552–53 and made a Privy Councillor in Aug. 1553.He was the last Treasurer of Calais from April 1554 to December 1557 and Comptroller of the Household from December 1557 to November 1558.He was elected a Member (MP) of the Parliament of England for Suffolk in 1547 and 1558, for Gatton in October 1553 and Grampound in April 1554.