He was the son of Victoria Marie (Javeaux) and Wallace Richard Ellender, Sr.[9] He attended public and private schools, and in 1909 he graduated with a Bachelor of Arts degree from the Roman Catholic St. Aloysius College in New Orleans.

[13] After surgery and recovery, Ellender inquired through his Congressman about obtaining a commission in the Army's Judge Advocate General Corps, and was offered a commission as an interpreter and translator in the United States Marine Corps, which he declined over concerns that because he spoke Louisiana French, he might not be proficient enough in the formal French language.

[13] Despite attempts lasting into the late 1920s to secure an honorable discharge as proof of his military service, Ellender was unsuccessful in obtaining one.

[15] As his career progressed, his biography often included the incorrect claim that Ellender had served as a sergeant in the United States Army Artillery Corps during the war.

He was floor leader from 1928 to 1932, when in 1929 he worked successfully against the impeachment forces, led by Ralph Norman Bauer and Cecil Morgan, that attempted to remove Governor Huey Long for a litany of abuses of power.

The committee voted on party lines to clear Bilbo, with the three Democrats siding with the Mississippi demagogue while the two conservative Republicans, Bourke Hickenlooper of Iowa and Styles Bridges of New Hampshire, dissented from the verdict.

[citation needed] Ellender served as the powerful chairman of the Senate Agriculture Committee from 1951 to 1953 and 1955 to 1971, through which capacity he was a strong defender of sugar cane interests.

Ellender was an opponent of Republican Senator Joseph McCarthy of Wisconsin, who had achieved national prominence through a series of well-publicized speeches and investigations attacking supposed communist infiltration in the US government, army and educational institutions during the 1950s.

In the aftermath of the Duck Hill lynchings, he also helped block a proposed anti-lynching bill which had previously been passed in the House, proclaiming, "We shall at all cost preserve the white supremacy of America.

In Southern Rhodesia he spoke to the media and was reported by a newspaper to have said he did not believe African territories were ready for self-governance and "incapable of leadership" without the assistance of white people.

Six days after the election, Johnston was appointed to finish Ellender's remaining term to gain a seniority advantage over other freshman senators.