John P. Cassidy (1855 – July 3, 1891) was an American right fielder in Major League Baseball from 1875 to 1885.

Growing up, Cassidy was an amateur pitcher in his hometown of Brooklyn, New York.

He started his professional baseball career with the Brooklyn Atlantics of the National Association in 1875.

[1] That season, he had a 1–21 win–loss record, a 3.03 earned run average, and 9 strikeouts.

[2] Cassidy continued his career as a right fielder, playing in the majors every season through 1885.