In late 1934, he became associated with Major Malcolm Wheeler-Nicholson's fledgling company National Allied Publications, later known as DC Comics.

[1] He also sketched "rough cover layouts for DC's top titles," including notably some for "Batman and Detective Comics until about 1946.

Featuring artwork primarily from Sheldon Moldoff and Joe Giella, Ellsworth wrote the strip between 1966 and 1970, whereupon E. Nelson Bridwell took over for a couple of years.

He initially objected to casting of Kirk Alyn as the lead, whom producer Sam Katzman had found by looking through studio photographs.

[4] In 1958, he created a pilot titled Superpup, which attempted to capitalise on that series' success by recasting the Superman mythos in a fictional universe populated by dogs instead of people.

[1] He is listed as having been – for "one week only" – a consultant on the 1966 Batman TV series (with Adam West), and a writer for the Superman radio show during the war years.