Thomas James O'Malley (July 22, 1868 – May 27, 1936) was an Irish American railroad conductor, union delegate, and Democratic politician from Wisconsin.

As a young man he went to work at several odd jobs, including hotel clerk and news agent, before becoming employed in the railroad industry.

That Summer, O'Malley announced he would seek the Democratic Party nomination for Lieutenant Governor of Wisconsin.

His time as acting governor coincided with an escalating banking crisis in the midst of the Great Depression.

[3] As presiding officer of the Senate, he case a number of tie-breaking votes against his party's priorities, often finding common cause with the progressive Republican faction.

[6] O'Malley continued to frustrate members of his party's leadership and often acted in concert with the new Progressive majority under Governor Philip La Follette.

Their eldest son, Thomas D. P. O'Malley, served three terms in the U.S. House of Representatives, later he was a federal appointee in the U.S. Department of Labor.