Born in Philadelphia, McCartee entered Columbia University, New York, at the age of 14 and graduated from the University of Pennsylvania Medical School at 20. Arriving in Ningpo in 1844 under the Presbyterian Board, he was probably the first Protestant missionary, and certainly the first physician, to reside on Chinese soil following the First Opium War. (See also Peter Parker.) In addition to his medical work, he became an adviser and interpreter for American officials and was later vice-consul in Chefoo (present-day Yantai) and Shanghai. In this capacity he helped persuade the "Heavenly King" of the Taipings to promise "non-molestation not only to Americans and Christians, but to all Chinese in their employ."
On a Chinese government assignment to Japan, McCartee remained in Tokyo as professor of law and science at the Imperial University (now Tokyo University), curator of the botanical gardens, and later secretary to the Chinese Legation there. In 1879 he advised General Ulysses S. Grant, the former U.S. president, mediating on the Loochoo (Ryukyu) Islands, although both China and Japan rejected his compromise. From 1885 to 1887 McCartee served as counselor to the Japanese Legation in Washington. After this he was reappointed by the Presbyterian Board as a missionary to Japan. He died in San Francisco.