John Gregg may refer to:

• John Gregg (Guildford MP) (died 1431 or after), English MP for Guildford
• John Gregg (Texas politician) (1828–1864), American politician from Texas who was killed in action during the American Civil War
• John R. Gregg (born 1954), American politician from Indiana

• John Gregg (bishop of Cork) (1798–1878), Anglican Bishop of Cork, Cloyne and Ross, 1862–1878
• John Gregg (archbishop of Armagh) (1873–1961), Anglican Archbishop of Armagh 1939–1959

• John Irvin Gregg (1826–1892), United States Army general
• John Robert Gregg (1867–1948), Irish-born American inventor of Gregg shorthand
• John P. Gregg (1876–1963), head football coach at Louisiana State University, 1899
• John William Gregg (1880–1969), American landscape architect
• John Gregg (1899–1986), companion of philanthropist Robert Allerton
• John Gregg (baker) (1909–1964), British founder of Greggs bakery
• John Gregg (actor) (1939–2021), Australian actor
• John Gregg (loyalist) (1957–2003), Ulster loyalist, member of the UDA

• John Gregg Fee (1816–1901), founder of Berea College
• John Greig (disambiguation)