He served as a fish culturist and clerk in the United States Bureau of Fisheries at Woods Hole, Mass., from 1900 to 1905, and also engaged in newspaper reporting in Boston and New Bedford.

He was a member of the State House of Representatives in 1905, elected as a Republican to the Sixty-Fourth and to the three succeeding Congresses, where he served from March 4, 1915, to August 21, 1922, when he resigned to accept a judicial position.

Walsh thought the creation of a committee would be yielding to "the nagging of iron-jawed angels" and referred to the women picketing Woodrow Wilson's White House (the Silent Sentinels) as "bewildered, deluded creatures with short skirts and short hair.

[1] (The use of steel to hold open the jaws of women being force-fed after the Silent Sentinels arrests and hunger strike is also one of the film's plot points.)

Walsh was appointed a justice of the Superior Court of Massachusetts on August 2, 1922, where he served until his death.