Kenneth Ernst studied at the Art Institute in Chicago, and became a prestidigator afterwards. In 1936, he joined the Harry "A" Chesler shop, where he cooperated on Star Comics and Funny Pages until 1943. He was also present at National Periodical Publications with 'Larry Steele' and at Western Publishing, with 'Buck Jones', 'Tom Mix', 'Clyde Beatty' and 'Magic Morro'. Between 1940 and 1942 he cooperated on the daily 'Don Winslow of the Navy' strip.
In 1942 he took over the 'Mary Worth' strip from Dale Ulrey, which he continued until his death in 1985. Ernst drew the strip, scripted by Allen Saunders, in a realistic style that had seldom been used in comics before, setting it apart from the more violent wartime comics. 'Mary Worth' became the prototype for a new style of gentle and sophisticated soap opera strip. The strip was eventually taken over by Allen's son, John Saunders, and artist Joe Giella, and it is still running today.