Marsh served as a marine in the first world war and his cartooning career is reported to have started around 1922. His first Dan Dunn episodes were probably published as Detective Dan in the LA Times from 1932, the first Dick Tracy imitator.

In 1933, Marsh produced Detective Dan: Secret Operative No. 48, an early tabloid-size comic, printed black-and-white on newsprint, with a three-colour cardboard cover. It is probably the first single-character comic with original art sold on US newsstands. The character became the syndicated daily newspaper strip Dan Dunn (from Monday 25 September 1933) followed by a Sunday page (until Sunday 3 October 1943).

The strip was popular and spawned a radio show and the 'Marsh Cartoon School' promising 'Success--fame--real money may be yours when you learn the easy simple methods and secrets which make the Marsh cartoons so successful' (Popular Mechanics, May 1935). The strips were reprinted in many comics (Dell, Eastern Color and Western in the US; Oddvar Larsen in Norway; Mon Journal in France) and adapted into seven Big Little Books.

Marsh went into the military in 1942. Allen Saunders took over writing Dan Dunn, with artwork initially by Paul Pinson and later Alfred Andriola until existing distribution contracts ran out on 3 October 1943.

After Marsh had returned from the war in 1946, he created Hunter Keene, another Dick Tracy-style daily newspaper strip (15 April 1946 to 12 April 1947).

This was followed by the western/frontier strip Danny Hale (from 27 October 1947). When King Features dropped the series, Marsh began self-syndicating from 15 January 1951, from an address in Chicago.

In 1952, Marsh changed the strip’s title to Dan'l Hale, with the lead character aged to a young man. Marsh aggressively marketed the strip through personal appearances, devoting significant time to selling the strip. He retained many of its King Features clients and more, particularly smaller papers. The strip continued until 13 October 1962, with Marsh becoming an activist against syndication.

Atlas Publications in Australia reprinted some strips of Hunter Keene (~1949) and Danny Hale (~1950-1951).

Marsh is reported to have worked as a prizefight manager, sailor, pilot, speculator and detective.