In 1885 he was admitted to the bar of Middlesex County and commenced practicing law in Concord, Massachusetts.

Though from a prominent Republican family Hoar was a Mugwump, leading the Young Men's Democratic Club of Massachusetts during Grover Cleveland's 1884 campaign, and was a member of the House of Representatives in the Fifty-second U.S. Congress (1891–1893).

Hoar was director of the Massachusetts Volunteer Aid Association during the Spanish–American War, and served[clarification needed] in several US Army hospitals in the South.

][1] After an illness of three weeks, Sherman Hoar died at his home on Main street, Concord, of typhoid fever contracted while making a tour of the Southern camps as a General of the Massachusetts Volunteer Association.

[2] Sherman Hoar came from a line of distinguished Massachusetts and New England politicians, lawyers and esteemed public servants.