Shearn began a highly successful private practice in 1893, and soon became an attorney for William Randolph Hearst.

[1] In 1914 Shearn was appointed as a justice of the New York State Supreme Court for the First District, based in Manhattan.

In 1924 Shearn was counsel for the Transit Commission in the New York City Subway investigation conducted for Governor Al Smith by Supreme Court Justice John V. McAvoy, who found Mayor John F. Hylan responsible for subway congestion and exonerated the Transit Commission.

As president of the New York City Bar Association from 1935 to 1937, Shearn was an initiator of the investigation into the ambulance-chasing racket.

Shearn died of a cerebral hemorrhage on February 12, 1953 at the age of 83 in New York City.