John or Jack Grundy may refer to:

• John Grundy (television presenter) (born 1946), English television presenter and author
• John Grundy Sr. (c. 1696–1748), English land surveyor and civil engineer
• John Grundy Jr. (1719–1783), English civil, drainage and canal engineer
• Jack Grundy (footballer) (1873–?), English association footballer
• Jack Grundy (rugby league) (1926–1978), English rugby league player
• John Clowes Grundy (1806–1867), English printseller and art patron
• Jack Grundy (cricketer) (born 1994), English cricketer