Robert McCay was born to Maude and Winsor McCay, the latter being a well known cartoonist and animator. Bob he had only one sister, Marion McCay and very early on their life, they moved to New York. He was an student at the Pratt Institute until the age of 19 when he enlisted in the National Guard and by the age of 21 he was called to the American Expeditionary Force during World War I. For his service, McCay was awarded the British Imperial Military Medal and the Distinguished Service Cross.
He returned home in 1919 and married Theresa Munchausen, and the couple had two kids. He died of cancer at the age of 66.
Bob McCay was a professional cartoonist who worked as a colourist for DC Comics during the early years of the company until 1945. McCay usually worked with his father as a letterer and inker until his father's death in 1934. After this he worked for companies such as DC and Fawcett Publications on titles like Batman and Bulletman.