Born in Ireland, Starkweather was adopted by a Connecticut family at a young age.
He studied at the Academie Colarossi in Paris in 1899 and later taught at the St. George’s School for Boys in New York while creating illustrations for popular novels.
He studied at the Art Students League in New York City, with Kenyon Cox, J. Carroll Beckwith and John Henry Twachtman.
In 1904, he went to Spain and became friends with Sorolla who influenced Starkweather’s fascination with dappled light and the effects of shadow.
In 1909, Sorolla introduced Starkweather to Archer Huntington and for the next seven years he was assistant curator of paintings at the Hispanic Society in New York. He subsequently taught at various New York City art schools, including Cooper Union, Hunter College, the Pratt Institute, and the Traphagen School of Design. Among his students were many artists who enjoyed a high degree of popularity including Luigi Lucioni, Paul Cadmus, and Wilfred Conrow.
Starkweather was a member of the American Watercolor Society, the Society of Independent Artists, Allied Artists of America, and the New York Watercolor Club.
His work is represented at the Metropolitan Museum of Art, the Brooklyn Museum, the Hickory Museum, the San Diego Museum, the Tides Institute, Yale University, and the New York Hispanic Society.