Rondthaler received his first small printing press at the age of 5, thus starting his career in the graphic arts. Working in New York in the 1930s, he associated with Harold Horman of the Rutherford Machinery Co. Together they adapted a step-and-repeat machine (for texture and metal printing) for photographic lettering, and in 1936 founded Photo Lettering Inc.
In 1969, Rondthaler associated with Aaron Burns and Herb Lubalin in founding the International Typeface Corporation. For several decades, ITC furnished manufacturers of photographic, electronic and laser equipment, a plethora of superb typefaces.
In later life, Rondthaler became interested in promoting the spelling reform of the English language as a means of fighting illiteracy. He was also an avid historian.
Rondthaler credited his long and healthy life to clean living, good genes, and regular cold showers. In an interview with CNN Ed stated "When my brother in 1918 came home from the army, he said, 'Ed, whenever you take a hot shower, end it with an ice cold one and count to 100. When your older brother tells you to do something, you do it," he said.
Rondthaler wrote a weekly letter to the editor of the local newspaper. Formerly very active in his community, for reasons of health he moved to Utah in 2008 to be closer to his family. He died of natural causes in Utah on August 19, 2009 at the age of 104.
Edward Rondthaler was the son of Howard Rondthaler, a Moravian bishop and president of Salem College in Winston-Salem, North Carolina, and his wife Katharine Boring, the daughter of a Philadelphia pharmacist. His grandfather (Rev. Edward Rondthaler) was a Moravian church bishop. Rondthaler spent his youth in Salem, North Carolina.
Rondthaler married Dorothy (Dot) Reid in 1930. They were married for 72 years up until her death in 2002. The Rondthalers had 3 sons. He lived in his Sears Roebuck home in Croton-on-Hudson from 1941 until 2008. He and his wife bought the home from Emer Yeager and Olga D’ Allaz Yeager for the sum of $7000. They paid off the mortgage on the house in 1946.