Mayer's career in the days before comic books was a diverse one. He worked as writer and artist on "scores of titles" for a juvenile audience circa 1932-33, before joining the Fleischer animation studios as an "opaquer" in 1934.

He began working for National Allied Publications (Major Malcolm Wheeler-Nicholson's initial company, later known as DC Comics) shortly after it was founded, in 1935, writing and drawing stories and "thus becoming one of the very first contributors [of original material] to comic books."

Between 1936 and 1938, Mayer worked for Dell Comics, producing illustrations, house advertisements and covers for titles including Popular Comics, The Comics and The Funnies. Also in 1936, he joined the McClure Syndicate "as an editor working for comics industry pioneer M.C. Gaines." While working for the McClure syndicate, Mayer came across a strip which he "immediately fell in love with." He recalls that:

Rescued from the slush pile, the McClure-rejected strip had been similarly rejected elsewhere, but upon publication in Action Comics #1, Jerry Siegel and Joe Shuster's Superman became an overnight success, single-handedly kickstarting the Golden Age of Comic Books, and going on to become one of the most iconic characters ever.

Mayer recognised the character's potential from the start. Quoted in 1985, he recalls:

In 1939, "Gaines left McClure to enter into a partnership with [National Periodical Publications]," and Mayer went with him, becoming the first editor of the All-American Comics line, then run as a separate entity from National/DC, publishers of Superman and Batman. Mayer edited and participated in the creation of - among others - the Flash (in Flash Comics), Green Lantern, Hawkman, Wonder Woman and All-Star Comics, home to the Justice Society of America.

Among his non-superhero work, Mayer assisted with lettering and logo creation on several All-American titles, and drew a number of covers for the "Mutt & Jeff" reprints appearing in the companies flagship title All-American Comics (1939—1958). Having created the semi-autobiographical strip "Scribbly, the trials of a novice cartoonist," for Dell Comics in 1936, (where the character appeared in The Funnies #2-29 and Popular Comics #8-9), Mayer moved Scribbly to All-American Publications in 1939.

Soon after, the strip included the supporting character of "Ma" Hunkel, who would go on to become the Golden Age incarnation of the Red Tornado, with Mayer writing, penciling and inking the re-named Scribbly and the Red Tornado for All-American Comics between 1941 and 1944 (when All-American merged with National).

Mayer retired from editing in 1948, "to devote himself full-time to cartooning" he began to write and draw a number of humour comics for National, including the features The Three Mouseketeers, "Leave it to Binky, a teenage humor book... [and] Sugar and Spike." This last title proved to be one of Mayer's longest-lasting strips, starring two babies who could communicate in baby-talk that adults could not understand. Mayer even signed the stories he drew, something rare at National Periodical Publications in the late 1950s when Sugar and Spike debuted.

In the 1970s, when failing eyesight limited his drawing ability, he continued to work for National/DC, contributing scripts to the companies horror and mystery magazines, including most notably House of Mystery (from c. 1970 for nearly twenty years), as well as House of Secrets, Forbidden Tales of the Dark Mansion and Black Orchid, a character he created. In the fiftieth anniversary publication Fifty Who Made DC Great, Mayer is cited as "still writ[ing] and draw[ing] for the company that first published his great discovery, Superman, forty-seven years ago."

After successful cataract surgery, Mayer returned to drawing Sugar and Spike stories for the international market.

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