In his youth he served in the household of Thomas, Duke of Clarence and joined him when his army crossed into Normandy in August 1412.
Cromwell served Henry V at the Battle of Agincourt in 1415, and throughout the reign he continued fighting in France.
Cromwell began legal proceedings against Tailboys, but was blocked by Suffolk, against whom Cromwell seemingly began impeachment proceedings.
Tailboys was sent to the Tower of London and later convicted in February 1450.
A Privy Councillor from 1422, he served as Treasurer of England (1433–1443) and twice as Chamberlain of the Household (1425–14–1455) during the reign of Henry VI.