[4] He attended the United States Military Academy in West Point, New York, and Washington and Lee University in Lexington, Virginia.

[12][13] In 1966, Johnston hired Ralph Perlman to the legislative staff; he was a business graduate of Columbia University in New York City.

[14][15] In 1970, State Senator Johnston outlined his proposal for a toll road to connect Shreveport with South Louisiana, as there was no north–south interstate highway at the time.

"[17] Johnston narrowly lost this race by 4,488 votes to Edwin Edwards in the runoff election of the Democratic primary.

[19] Ellender died during the campaign,[19] and Johnston, with powerful name identification stemming from his gubernatorial bid months earlier, won the primary easily.

McKeithen, the first Louisiana governor to serve two consecutive terms, left office six months prior to the Senate election in order to conduct his campaign.

[21][22] The creation of the interim position was done to swear in Johnston immediately upon certification of his election, allowing him to gain an edge in seniority over other senators who first took office during the 93rd Congress.

For a time, Johnston's director of special projects was James Arthur Reeder (1933–2012), a former Shreveport and Washington, D.C., attorney, and owner of a chain of radio stations.

Johnston's closest re-election race was in 1990 against State Representative David Duke, a former Ku Klux Klan man and Republican candidate, who was not endorsed by his party's leadership.

Louisiana State Senator Ben Bagert of New Orleans dropped out of the primary race in a bid to try to prevent a runoff battle between Johnston and Duke.

[29] These included Ted Stevens and Frank Murkowski of Alaska, David Durenberger and Rudy Boschwitz of Minnesota, John Danforth of Missouri, William Cohen of Maine, Warren Rudman of New Hampshire, and Nancy Kassebaum of Kansas.

[32][33] He also broke ranks to support the narrowly achieved confirmation of Clarence Thomas as associate justice of the United States Supreme Court.

[35] Johnston was one of the few Senate Democrats to vote against the Budget Act of 1993, which was strongly supported by President Bill Clinton.

He repeatedly voted against the Balanced Budget Amendment and giving the President the line-item veto, both of which were measures strongly favored by fiscal conservatives in both parties.

Johnston was the only member of either house of Congress to vote against a 1995 resolution to allow Taiwan's president Lee Teng-hui to visit the United States.

Johnston and Long gained authorization[clarification needed] of the Cane River National Heritage Area in Natchitoches Parish in 1994, which stimulated tourism in the region.