Seward was a native of Florida, New York, and was educated at the S. S. Seward Institute. He attended Union College; he later served as a trustee of the school and was awarded the honorary degree of LL.D. In 1861, he was appointed to the position of U.S. Consul in Shanghai, an appointment secured through his uncle William H. Seward, who was serving as United States Secretary of State. He was appointed United States Consul General in Shanghai in 1863, and U.S. Minister to China on January 7, 1876.