McCarthy was born on July 24, 1863 in Boston, Massachusetts, the eldest son of Daniel and Sarah McCarthy. McCarthy joined the Boston Reds in the Union Association in as a starting pitcher and outfielder. In limited innings and at-bats, he played poorly, batting at a paltry .215 average, and lost all seven of his pitching appearances. McCarthy moved to the National League and played with the Boston Beaneaters the following season and the Philadelphia Quakers the following two years but failed to bat higher than .200 in any season, although in limited at-bats.