John Cassidy may refer to:
John Cassidy (artist) (1860–1939), Irish sculptor and painter
John Cassidy (baseball) (1855–1891), American baseball player
John Cassidy (basketball) (born 1947), Canadian Olympic basketball player
John Cassidy (journalist) (born 1963), business journalist and published author
John Cassidy (magician) (born 1967), American magician and balloon artist
John Cassidy (author), American author and publishing executive
John Cassidy (chancellor), Australian businessman and former university chancellor John Cassidy (seismologist) (born 1959), Canadian seismologist John Cassidy (speed skater) (born 1952), Canadian Olympic speed skater Jack Cassidy (1927–1976), American actor John Edward Cassidy (1896–1984), American lawyer; Illinois Attorney General John E. Cassidy Jr (1924—2003), member of the Illinois House of Representatives. John F. Cassidy, Vice Chairman of the board and former Chief Executive Officer of Cincinnati Bell Inc. John Joe Cassidy (died 1995), Gaelic football player for Cavan John P. Cassidy (1912–?), Los Angeles City Council member, 1962–1967