Thomas McIntyre Cooley was born in Attica, N. Y. on January 6, 1824. In 1842, after having graduated from the Attica Academy, Cooley began the study of law in Palmyra, N. Y. He came to Adrian, Mich., in September, 1843 where he completed his law studies with the firm of Tiffany & Beaman. He was admitted to the bar in January, 1846. He briefly practice law in Tecumseh, then returned to Adrian in 1848 becoming member of the firm of Beaman, Beecher & Cooley. In 1855, he formed a partnership with Charles M. Croswell.
In 1857 Cooley was chosen by the Michigan legislature to compile the laws of the State. In January, 1858, he was appointed reporter of the Supreme Court, and while in that position edited and published eight volumes of reports. In 1859, with the establishment of the Law Department of the University of Michigan, Cooley was chosen, along with Judge J. V. Campbell and C. I. Walker, to be one of the three professors in the new department.
In 1864 Cooley was elected a Justice of the Supreme Court, and was re-elected in 1869 and in 1877, continuing in that position until his defeat in 1885. During this same period he continued his teaching and writing. In 1884, he resigned his professorship in the law department to accept the position of professor of American history and constitutional law in the Literary Department of the University of Michigan.
In the mid-1880s, Cooley became involved as an arbitrator in disputes involving the railroad. In 1887, President Cleveland appointed Cooley to the newly organized Interstate Commerce Commission, where he served as chairman. He served for four years resigning in September 1891. He died in Ann Arbor, Michigan, September 12, 1898.