Thomas MacDonald Patterson was born in County Carlow, Ireland on November 4, 1839, but his family emigrated to the United States when he was a boy, and they settled in New York City in 1849.

A few years later, they moved to Crawfordsville, Indiana, where the young Patterson found work in a printing office and with a watchmaker and jeweler.

Patterson's political career began when he became a member of the Democratic National Committee in 1874 (a post he held until 1880).

During these years, Patterson was twice an unsuccessful Democratic candidate for Governor of Colorado including in 1888, when he was defeated by Republican Job Adams Cooper.

Patterson returned to national politics in 1900 when he was elected as a Democrat to the United States Senate, serving a single term (1901–1907) and refusing to stand for re-election.