John Thomas "Jack" Brennan (1877–1950) of the Montreal Shamrocks Lacrosse Club. Brennan was also a hockey player with the Shamrocks, representing the club as a cover point in the CAHL and ECAHA between 1901 and 1908.

Jack Brennan is not to be confused with similarly named Montreal Shamrocks rover Jack (John Patrick) "Doc" Brannen who won Stanley Cup championships with the club in 1899 and 1900.