By 1918, Harris was working as a broker and in 1919 purchased a seat on the New York Stock Exchange, as a member of Robinson, Duff, and Company. He made a good living working with the Stock market exchange. During his days working in theater, Harris had struck up an acquaintance with J. Robinson Duff, formerly a heavyweight boxer who had turned to Wall Street to make a living. Duff encouraged Harris to learn the ropes of trading stocks. Harris continued working as a wall street broker through 1949, with a specialty in international securities.Silver, Mike, Stars in the Ring, Jewish Champions, (2016) Rowman and Littlefield, Guilford, Connecticut, pg. 49 Long after his boxing retirement, he continued to gently spar with and mentor young boxers to maintain his conditioning. One of the young boxer's Harris sparred with was future heavyweight champion Gene Tunney.
