Westchiloff was born in Russia on 15 December 1878. He latinized his name to Constantin A. Westchiloff when he emigrated to Western Europe in 1922.
He studied under Ilya Repin at the Imperial Academy of Arts in St. Petersburg from 1898. He won an award in 1904 for the painting, "Ivan the Terrible After the Triumph of Kazan." He held a foreign study fellowship from the Royal Academy in 1905-06. He exhibited in the Royal Academy's Fall Exhibit of 1906, showing "Breakthrough of the Cruiser Askold in 1904 in the Yellow Sea," which documented the Russo-Japanese War. In that Academy exhibit he also showed portraits of Count Nikolay Muravyov-Amursky and of Lieut. S. Poguljajeff. He was also active in theatre design at the Petrograd Technical Institute.

He emigrated from Soviet Russia in 1922, lived in Italy (1923-1928), France (1929-1935), and immigrated to the United States in 1935 and settled in New York City, where he died.

Throughout his career Westchiloff painted a wide variety of subjects in the Impressionist style, but was particularly noted for his seascapes and harbor scenes. He operated a studio in New York and often painted coastal Maine scenes. What may be his largest work, "Niagara Falls" at 57-inches wide by 48-inches high, appeared at auction in London in the early 1980s and is now in a private collection in Chicago.