John B. Johnston (born June 10, 1932), is a Washington, D.C.-based lobbyist who was a U.S. Democratic Party politician and United States senator from Louisiana from 1972 until 1997.
Johnston, born in Shreveport, Louisiana, graduated from C.E. Byrd High School. He attended the United States Military Academy. Johnston was very narrowly elected in an at-large campaign to the Louisiana State House of Representatives in 1964, along with two Republicans, Morley A. Hudson and Taylor W. O'Hearn, and two other Democrats from Caddo Parish, Algie Brown (1910-2004) and Frank Fulco, Sr.
He moved up to the Louisiana Senate in 1968, having secured a solid victory in the general election. Johnston ran for governor of Louisiana in 1971 and lost very narrowly to Edwin Washington Edwards in the Democratic Party runoff election.