William was the direct male-line descendant and heir of Sir John Mundy, who first bought the manors of Markeaton (the principal seat of the Mundys), Allestree and Mackworth in 1516 from Lord Audley.

Though his paternal ancestors had held all of the aforementioned manors, William inherited only Markeaton as all of the other manors had been sold by his paternal grandfather Francis Noel Clarke Mundy (Osbaston in 1766 and Allestree in 1781 to Thomas Evans).

As such he was also a direct descendant of the Plantagenet Kings preceding Edward III, as well as William the Conqueror, the Dukes of Normandy and of Alfred the Great.

He was then member of parliament for the South Derbyshire constituency with Charles Robert Colevile from 1849 to 1857 and again with Thomas William Evans from 1859 to 1865.

In 1856 he was the President of Derby Town and County Museum and Natural History Society.