Following his brief tour in the Navy, Poage attended the University of Texas at Austin, the University of Colorado at Boulder, and Baylor University in Waco, Texas. He received his A.B. from Baylor in 1921. He worked as a farm hand from 1920-1922, after which he taught geology at Baylor from 1922-1924 while working on his law degree. Receiving his LL.B. in 1924, Poage was admitted to the bar that year. While practicing law in Waco, Poage taught at the Baylor Law School from 1924-1928.

Poage's first experience in public life came with his election to the Texas House of Representatives in 1924. After four years service, Poage left politics for a time but returned to Austin as a state senatorfrom 1931-1937. While in the state senate, Poage made an unsuccessful attempt to unseat 11th district congressman O. H. Cross in the 1934 Democratic primary. However, his second effort in 1936 succeeded, and he entered the powerful Texas delegation in Washington.

Establishing himself as a supporter of the New Deal, Poage worked exhaustively for rural electrification and rural telephone service during the 1930s and 1940s. Poage's tenure coincided with the rise to power of many fellow Texans, including Lyndon Johnsonand Sam Rayburn. Along with most other Texas congressmen, Poage opposed the efforts of the "Dixiecrats" in the late 1940s and remained loyal to the Truman administration.

Poage's increasing political stature led to his being suggested as a candidate to succeed Senator Tom Connally in 1952. Instead, Poage remained in the House building up power and influence through seniority. Despite the defections of many prominent Texas Democrats, such as then Governor Alan Shivers, to the camp of Republican Dwight Eisenhower, Poage steadfastly supported the Democratic ticket, advising Adlai Stevenson's campaign on farm issues and Texas politics in 1952 and 1956.

With the election of John Kennedy to the presidency in 1960, Poage was the favorite of influential Texans in Washington, as well as southern Democrats, to become the Kennedy administration's Secretary of Agriculture. However, Poage bowed out of consideration. In 1967, following the election defeat of Rep. Harold Cooley of North Carolina, Poage became chairman of the House Agriculture Committee, holding that position until 1974.

Poage's agricultural expertise and safe Democratic district allowed him to become one of the party's travelling campaign speakers in farm state congressional campaigns, throughout the 1960s and 1970s.

In 1972, rumors circulated concerning Poage's possible retirement, leading several rivals to enter the Democratic primary against him. After a campaign in which Poage's age became an issue, the congressman easily defeated his opponents and went on to win an uncontested general election victory. As for Republican opponents, Poage faced them only four times: in 1964, 1966, 1974, and 1976. The 1976 race, against Waco businessman Jack Burgess, was the closest, though Poage still won with 57% percent of the vote. In 1977, the Washington veteran announced his retirement, resigning in December, 1978 prior to being succeeded by a former aide, Marlin banker Marvin Leath.

In 1979, the W. R. Poage Legislative Library for Graduate Studies and Research was dedicated on the Baylor University Campus to house not only Poage congressional papers, but also papers of eight other former U. S. Congressmen. In addition, the Baylor Collections of Political Materials includes papers of former Texas State legislators, former judges, and numerous ancillary papers.

After his retirement, Poage kept an office in the Baylor building that bore his name. He spent his leisure time in personal pursuits such as authoring an autobiography, My First Eighty-five Years(1985), and writing four books on local history and politics: After the Pioneers (1969), Politics Texas Style (1974), McLennan County Before 1980 (1981), How We Lived (1985). Poage died in Temple, Texas on January 3, 1987 and was buried in Waco.