He graduated at College of Charleston in 1840, studied law at Harvard University, and was admitted to the bar in 1843.

[2] He was married to Eliza Natalie Cuthbert, whose family had land originally granted by King George II.

[1] He was a member of the state legislature in 1862–1866, and served as colonel on the staff of General Roswell S. Ripley during the Civil War; and later returned to Washington.

[2] He was counsel for the United States before the Halifax Fisheries Commission in 1877; was commissioner for the revision of the treaty with China in 1880; was minister to Chile in 1881 and 1882; in 1882 with General Ulysses S. Grant negotiated a commercial treaty with Mexico; and in 1889-1890 was a delegate to the Pan-American Congress in Washington.

[2] In the opinion of historian David Saville Muzzey, Trescot was "one of the most accomplished diplomats in our history.