Robinson was elected to the Arkansas legislature in 1894.
In 1913 he became Governor of Arkansas and resigned his Congressional seat. Twelve days after becoming governor, Robinson was chosen to become a United States Senator, replacing Senator Jefferson Davis after his death. He resigned his position as governor in March of 1913. Robinson was the last Senator chosen by a state legislature rather than direct election.
Though he only served for a short time as governor his administration focused on providing funds to complete the new state capitol building, creating a labor statistics board, adopting an official state flag, and working to create a highway commission.
Robinson was reelected four times to the Senate. He was selected to be Senate Majority Leader in 1922 and held that position until his death. Robinson was a leading spokesman for President Franklin Delano Roosevelt's New Deal legislation and his court-packing plan in 1937. Robinson's death effectively killed off the Roosevelt Administration's propoosal to reshape the United States Supreme Court.
Robinson is the namesake of, Camp Joseph T. Robinson, Arkansas's primary National Guard base and Robinson Arena in downtown Little Rock. Robinson's face appears on the front of the United States half dollar produced for the 1936 Arkansas Centennial; he was one of only four living men to appear on a US coin.