Born in Aiken, South Carolina, he learned the sport of polo from his parents, Louise and Thomas Hitchcock, Sr. His father was a U.S. Racing Hall of Fame horse trainer who had been a 10-goal player who helped found the Meadowbrook Polo Club on Long Island, New York and who captained the American team in the inaugural 1886 international Westchester Cup. Tommy Jr. played in his first tournament at age 13 and was part of the Meadowbrook Polo Club that won the 1916 U.S. national junior championship.
During World War I, at age 17 Tommy Hitchcock joined the Lafayette Escadrille flying corps in France. He was shot down and captured by the Germans but escaped his captors by jumping out of the train. On foot, he hid in the woods during the daytime then walked more than one hundred miles for eight nights to the safety of Switzerland. 
After the war, Hitchcock returned to study at Harvard University. Playing polo, he led the U.S. team to victory in the 1921 Westchester Cup. From 1922 to 1940, Hitchcock carried a 10-goal handicap, which is the highest ranking in polo, from the United States of America Polo Association. Playing with notable stars such as Pete Bostwick, Jock Whitney, and Gerald Balding, he led four teams to U.S. National Open Championships in 1923, 1927, 1935 and 1936.
Author F. Scott Fitzgerald loosely modeled two characters in his books on Tommy Hitchcock, Jr.: Tom Buchanan in The Great Gatsby (1925) and the Tommy Barban character in Tender Is the Night (1934).
Hitchcock married Margaret Mellon, daughter of William Larimer Mellon, in New York City on 15 December 1928. They had four children: daughters Louise Eustis Hitchcock, Margaret Mellon Hitchcock, and twins Thomas Hitchcock III, and William Mellon Hitchcock.
A friend of fellow polo player, Robert Lehman, in 1937 he become a partner in the Lehman Brothers Wall Street investment firm.
Serving as a Lieutenant Colonel in the United States Army Air Force in World War II, Hitchcock was assigned as an assistant air attache to the US Embassy in London, England. In that capacity, he was instrumental in the development of the P-51 Mustang fighter plane, particularly in replacing the original Allison engine with the Packard-built Rolls-Royce Merlin. He was killed in a crash while piloting one such aircraft near Salisbury, Wiltshire, England when he was unable to pull out of a dive while doing tests.
Following its formation, in 1990 Tommy Hitchcock, Jr. was inducted posthumously into the Museum of Polo and Hall of Fame.
Tommy with his "Baby" the P-51 Mustang