He was appointed Chancellor of the Exchequer by Henry VI in 1454 and again (for life) in 1456, which was confirmed in 1461 by Edward IV. He was reappointed in 1465 (possibly after illness) and finally resigned the post in 1469 to be replaced by Richard Fowler. He then served the future Richard III as a counsellor.
He died in 1489 and was buried at Sheriff Hutton church where he had endowed a chapel. He had married Agnes Thweng of Cornburgh but left no surviving children. However, his will of 1474 left money to several grandchildren.
- "Thomas WYTHAM (WITHAM) (d.1481)". Retrieved 2011-12-07.
- "Calendar of the Patent Rolls preserved in the Public Records Office". Retrieved 2011-12-07.
- "The Will of Thomas Witham of Cornburgh, Senior". Retrieved 2011-12-07.