Born 1846 in County Cavan and raised in Newark, New Jersey, Leonard is commonly recognized as the first native of Ireland to play in the major leagues. He was one of four who played during the first National Association season, so he owes the distinction partly to fortunate scheduling in the spring of 1871, partly to our counting the NA as a major league. (But it seems likely that Leonard and Fergy Malone both played in the first National League game, 22 April 1876.)