Patterson was born in County Carlow, Ireland, 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.
When the Civil War broke out in 1861, Patterson enlisted in the Eleventh Regiment of the Indiana Volunteer Infantry. He returned home in 1862, and went to college first at Indiana Asbury University (now DePauw University), then at Wabash College.
Patterson was admitted to the bar in 1867 and began his practice in Crawfordsville. In 1872, he moved to Denver, where he started a law practice and was city attorney in 1873 and 1874.
Patterson's political career began when he became a member of the Democratic National Committee in 1874 (a post he held until 1880). He was then elected as a Democrat to be a Delegate from the Colorado Territory to the 44th Congress (1875-76), stepping down when the Territory became a State. James B. Belford, a Republican, was initially elected as Colorado's first Congressman, but Patterson successfully contested his election and served in the U.S. House of Representatives in the 45th Congress (1877-79). Patterson chose not to stand for re-election in 1878.
After leaving Congress, Patterson resumed the practice of law in Denver, and purchased first the Rocky Mountain News in 1890 and later the Denver Times. During these years, Patterson was twice an unsuccessful Democratic candidate for Governor of Colorado.
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. While a senator, Patterson served on the Lodge committee that investigated alleged war crimes in the Philippine-American War.
After leaving the Senate, Patterson published his newspaper until his death.
Patterson's remains are interred in Fairmount Cemetery in Denver.