Born at 3 William Street, Kingsland Road. He became a Tunbridge Ware manufacturer, then a music teacher. He broadened his interests to the general education of working-class children and became the foundation headmaster of the Birkbeck Schools, set up by William Ellis using the London Mechanics Institute in Southampton Buildings near Holborn. Five other such schools followed, with Runtz's brothers George and James being headmasters at two of them. Runtz became the Superintendent of all the schools. The 1870 Education Act, 1870 made these schools unnecessary and by 1905 they had all closed or been taken over.
Runtz also worked in the business finance world, joining the boards and then becoming the chair of an insurance company and of a building society. He was also on the board of a number of other companies including the New River Company.
He entered local government in 1842. From 1867 he was the Stoke Newington Vestry's representative on the Metropolitan Board of Works on which he served for 22 years.
As well as the saving of Clissold Park, he was involved in the preservation of Hackney Downs, Mill Hill Fields, Newington Green and Finsbury Park. In these projects he often worked with Joseph Beck. He was also involved in the freeing of London bridges from tolls.
Our information is from Saving Clissold Park.