After an education in New York private schools, Whittemore spent three months in the winter of 1877 in the studio of the landscapist, William Hart. For the next few years, he worked in his father's business, where he learned gilding, and then spent several years between 1882 and 1886 in attendance at Academy antique and life classes, and also working at the Art Students League. In the late 1880s, he went abroad, entering the Acad‚mie Julian in Paris for study under Jules Lefebvre and Jean-Joseph Benjamin-Constant.
Whittemore married artist Alice V. Whitmore in 1895; they built a home in East Hampton, and made frequent trips to Europe. Proficient in landscape, genre, and still life, he gradually adopted portraiture (with ivory miniatures a speciality) as his main emphasis around the turn of the century. In the Academy's winter exhibition of 1917, he won the Proctor Prize for portraiture. Whittemore was a steady contributor to Academy exhibitions, his work appearing in annuals over a span of sixty years. He married his second wife, artist C. Helen Simpson, in 1921.
