Seeley was born in Stockbridge, Massachusetts, and studied painting at the Massachusetts Normal Art School in Boston for three and a half years beginning in 1897. During this time he met the photographer F. Holland Day. Seeley returned home as a artist-photographer in 1902.
Seeley first received attention as a photographer when he exhibited in the First American Salon of 1904. Alvin Langdon Coburn, one of the judges, introduced him to Alfred Stieglitz, who recognized Seeley's talent and invited him to join the Photo-Secession. From 1906 to 1910, Seeley was an active member of the group, and his work was exhibited in Stieglitz's gallery "291" and reproduced in Camera Work.
Early in his career Seeley declined an offer to head the art department at Pratt Institute. Instead, he remained in Stockbridge, where for 40 years he was chairman of the ushers at the First Congregational Church, and the supervisor of art in the Stockbridge public schools. Seeley was also an authority on birds, and was for many years associated with the Biological Survey of Washington, for which he maintained a landing station and reported bird migration. Toward the end of his life Seeley achieved recognition as a painter of brasses and coppers in still life canvases.