He was an accountant by profession.
He won the Manhattan Chess Club Championship ten times outright and once shared. In 1915, he tied for third/fourth place with Oscar Chajes, behind José Raúl Capablanca and Frank James Marshall in New York. In 1916, he tied for 2nd-4th with Dawid Janowski and Borislav Kostić, behind Capablanca, in New York. In 1923, he was equal first with Marshall in Lake Hopatcong. In 1924, he lost a match to Efim Bogoljubow (+1 -3 =2) in New York. In 1925 he drew a match with Carlos Torre Repetto (+1 -1 =4) in New York. In 1926, he finished 2nd, behind Capablanca, in Lake Hopatcong.
Kupchik played for the US team in the 6th Chess Olympiad at Warsaw 1935. He scored (+6 -0 =8) on third board, and won individual bronze medal and team gold medal. He played on Board 9 in the 1945 USSR-USA radio match, losing ½-1½ to Vladimir Makogonov.