In winning the seat, he replaced its former occupant, Lyndon B. Johnson, who had been elected that year for the first time to the United States Senate.

Thornberry was a member of the Rules Committee of the United States House of Representatives from January 1955 to his 1963 resignation, when he was appointed by Johnson, now President, to the federal bench.

[3] He was one of the majority of the Texan delegation to decline to sign the 1956 Southern Manifesto opposing the desegregation of public schools ordered by the Supreme Court in Brown v. Board of Education.

[4][5][6] Thornberry was present on Air Force One and witnessed Lyndon Johnson taking the oath of office following the assassination of President Kennedy.

He was confirmed by the United States Senate on July 15, 1963, and received his commission from President Lyndon B. Johnson on December 17, 1963.

[2] Thornberry was nominated by President Johnson on June 22, 1965, to a seat on the United States Court of Appeals for the Fifth Circuit vacated by Judge Joseph Chappell Hutcheson Jr.

[9] On October 4, 1968, after several days of contentious debate on the floor of the Senate, and with prospects for confirmation fading, Johnson withdrew the Fortas nomination.