Catesby was an aspiring lawyer who rose initially in the service of William, 1st Lord Hastings. He was a member of the Council that ruled during the reign of Edward V, serving as a spy for the Duke of Gloucester (soon to be Richard III). After Richard was enthroned, Catesby served as Chancellor of the Exchequer, and as Speaker of the House of Commons during the Parliament of 1484. He also received a substantial grant of land from the king, enough to make him richer than most knights.
Catesby became one of the few to enjoy King Richard's full confidence and Collingbourne summed up his importance in 1484 with his famous lampoon:
the Catte, the Ratte and Lovell our dogge
rulyth all Englande under a hogge
After the collapse of the Buckingham revolt and the death of his wife he warned Richard against any idea of marrying his niece, Elizabeth.
Catesby fought alongside Richard at the Battle of Bosworth and was captured. Alone of those of importance he was executed three days later. The suggestion that he might have done a deal with the Stanleys before the battle comes from his will when he asked them "to pray for my soul as ye have not for my body, as I trusted in you.