The Byrd machine, or Byrd Organization, was a political machine of the Democratic Party led by former Governor and U.S. Senator Harry F. Byrd (1887–1966) that dominated Virginia politics for much of the 20th century. From the 1890s until the late 1960s, the Byrd organization effectively controlled the politics of the state through a network of courthouse cliques of local constitutional officers in most of the state's counties.

"The organization" had its greatest strength in rural areas. It was never able to gain a significant foothold in the growing urban areas of Virginia's many independent cities, which are not located within counties, nor with the emerging suburban middle-class of Virginians after World War II. Byrd's vehement opposition to racial integration of the state's public schools, including a policy of massive resistance, which ultimately failed in 1960 after it was ruled unconstitutional by both state and federal courts, could be described as the organization's "last stand", although the remnants of it continued to wield power for a few years longer.

When the senator resigned in 1965, he was replaced in the Senate by his son Harry F. Byrd Jr. However, the heyday of the Byrd organization was clearly in the past. With the election of a Republican governor in 1969 for the first time in the 20th century, the 80 years of domination of Virginia politics by conservative Democrats ended.

After the American Civil War, Virginia's politics were chaotic. Initially, former Confederates were not allowed to vote, and factions of newly enfranchised black voters joined the electorate. In the late 1870s, a coalition of blacks, Republicans, and populist Democrats formed the Readjuster Party. Readjusters aspired "to break the power of wealth and established privilege" of the planter class elites who had controlled Virginia politics since the colonial era and to promote public education. It was led by Harrison H. Riddleberger (1844–1890) of Woodstock, an attorney, and William Mahone (1827–1895), of Petersburg, a former Confederate general who was president of several railroads.

The Readjuster Party's power was overturned in the late 1880s, when John S. Barbour Jr. (1820–1892) led the first Conservative Democrat political machine in Virginia, known as the Martin organization, aided by a poll tax enacted in 1902 that effectively disenfranchised blacks and poor whites. U.S. Senator Thomas Staples Martin (1847–1919) took over after Barbour died, but Senator Martin's political control was thin by the time he died in office in 1919. By this time, a young state senator from Winchester, Harry F. Byrd, was a rising star in state politics and the Democratic Party. He had served the Wilson Administration during World War I helping with gasoline rationing as a volunteer.

In 1922, with seven years of experience in the Virginia State Senate, Byrd gained statewide prominence by confronting Virginia's powerful lobby of highway builders. Byrd had gained a lot of related experience when earlier managing the Valley Turnpike. In the Virginia General Assembly, he led a fight against using bonded indebtedness as a method to pay for new roads. He feared the state would sacrifice future flexibility by committing too many resources to paying off construction debt.

In 1923, Byrd was sued for libel by the Virginia Highway Contractors Association because he said their activities "by combination and agreements may be very detrimental" to the State. The court dismissed the suit, stating the criticism was legal, imposing all costs upon the association. The publicity figuratively paved the way for the election of Harry Byrd to statewide office.

The Virginia Democratic machine, since the 1890s, had rigidly stood for restricted suffrage, balanced budgets, and regressive taxation. After the Constitution of 1902 effectively disenfranchised more than half the electorate, the organization had had little trouble winning most Virginia elections.