Narrowly defeated for governor of Louisiana in 1924, Long was swept into office four years later. When the state legislature obstructed his program of economic and social reform, he severely lessened the influence of the moneyed oligarchy that had dominated Louisiana government since Reconstruction and established his own control of the state through extensive use of patronage. Long was responsible for the building of badly needed roads and bridges, the expansion of state-owned hospitals, and the extension of the school system into remote rural regions. He also increased the taxes of large Louisiana businesses, especially the oil companies. The state legislature was bludgeoned or bought into passing his laws. In 1929, Long was impeached on charges of bribery and gross misconduct, but he was not convicted.

"The Kingfish," as Long was called, was elected to the U.S. Senate in 1930, but he did not take his seat until Jan., 1932, after he had assured the succession as governor of one of his own supporters. From Washington, Long continued to direct the Louisiana government. In 1934 he began a reorganization of the state, which virtually abolished local government and gave Long the power to appoint all state employees. As a senator, Long was at first a supporter of the New Deal, but soon became one of Franklin Delano Roosevelt's most vociferous critics.

A presidential aspirant, Long gained a steadily increasing national following. Early in 1934 he introduced his plan for national social and economic reform, the "Share-the-Wealth" program; it proposed a guaranteed family annual income and a homestead allowance for every family. Meanwhile, in Louisiana, Long continued to expand his powers. In Sept., 1935, on a trip to the state, Long was assassinated. The assassin, Dr. Carl A. Weiss, was slain by Long's bodyguards. Long's political machine flourished for several years after his death, and the Long family remained important in the state.