Queensland entered the new Commonwealth of Australia with the lowest voter endorsement (55 percent) of the proposed union of the six colonies. Southern Queensland vehemently opposed federation, fearing economic decline of its industries. The overwhelming enthusiasm of the working-class miners and shearers in the northern regions ensured success. On Jan. 1, 1901, the Commonwealth of Australia was proclaimed, creating the state of Queensland. The census of that year recorded 498,129 inhabitants, excluding Aborigines and Torres Strait Islanders.

In 1905 white women gained the right to vote, and plural voting (a system by which certain citizens were permitted to cast more than one vote) was abolished; compulsory voting was first enacted in Queensland in 1914, followed by the other states. In 1922, at the instigation of the ruling Labor government, the Legislative Council (upper house of the bicameral parliament) was abolished, leaving only the Legislative Assembly. Three years later Greater Brisbane was established as the largest municipal council in Australia, with a council elected by a full white adult electorate.

A radical Labor government (1915–19) led by the barrister Thomas Joseph (T.J.) Ryan brought state enterprises into competition with the private sector. The subsequent government led by the trade unionist Edward Granville (“Red Ted”) Theodore (1919–25) attempted unsuccessfully to establish heavy industry by promoting a state-owned smelter at Bowen. Later Labor administrations—under William McCormack (1925–29), William Forgan Smith (1932–42), Frank Cooper (1942–46), Ned Hanlon (1946–52), and Vincent Gair (1952–57)—were increasingly conservative and cautious.

The Labor government was replaced by a Country-Nationalist Party government in 1929, which came to power amid the rising unemployment, falling incomes, and social distress of the early years of the Great Depression. During its tenure, the Country-Nationalists abolished state trading and established the Bureau of Economics. In 1929 Irene Longman became the first woman to be elected to the Queensland Parliament. The government was unable to stem the tide of the depression and was replaced by the Labor Party, which attempted to stimulate the economy through large capital improvement projects. Several substantial projects were undertaken, such as construction of the Story Bridge over the Brisbane River in Brisbane, the Somerset Dam on the Stanley River, a tributary of the Brisbane, and the University of Queensland at St. Lucia. The worst of the depression was ending by 1934, and many social services suspended during the bad economic times were reinstituted. However, Queensland had not fully recovered when it became actively involved in World War II early in 1942. In July 1942 Gen. Douglas MacArthur, commander of the Allied forces in the Pacific, set up his headquarters in Brisbane. Hundreds of thousands of service personnel passed through the state on the way to the Pacific war zone, providing a sustained boon to the economy. After the war the government continued to improve public works and social services, inaugurating large-scale irrigation and hydroelectric projects such as the Burdekin River and Tully Falls schemes and introducing free hospital service in 1946.

In 1957 Labor, split by a schism that produced the Australian Democratic Labor Party, was ousted by a coalition of the Country and Liberal parties, which remained in power until 1988 (in 1974 the Country Party changed its name to the National Party). A six-year period of one-party rule by the National Party lasted from 1983 to 1989. During that time political influence in the police, judiciary, and electoral system became controversial, leading to an independent, wide-ranging inquiry. Reforms adopted include the creation of the independent and powerful Criminal Justice Commission and the Electoral and Administrative Review Commission.

Rule by the National Party ended with the Labor Party’s comprehensive victory in 1989 under Wayne Goss. Goss led an effort to reform the public service and made police and politicians more publicly accountable. A period of political uncertainty ensued in 1995, when an apparent Labor victory in July was reversed by the courts, and a National-Liberal coalition took office in early 1996. Labor returned to power in 1998 under Peter Beattie amid considerable voter discontent and alienation, but politics soon returned to its more usual contours. In the early 21st century the Labor government strove to redress Queensland’s continued reliance on primary production through a commitment to high-technology industries such as biotechnology and information technology, as well as filmmaking and music production. All of this development was located in the state’s southeastern corner. Beattie resigned in 2007 and was succeeded in office by Queensland’s first female premier, Anna Bligh.

Since the late 20th century, Queensland has been at the centre of major legal and social change in the country. A decision of the federal High Court in 1992 on native land title in the Torres Strait Islands (popularly called the Mabo case, named for the activist Eddie Koiki Mabo) overturned the previous concept of terra nullius (Latin: “the land of no one”), which had deprived the indigenous peoples of their customary property rights. The Wik case of 1996, involving Aboriginal claims, also heard in the High Court, ruled that native title could coexist with pastoral leases. As land is administered under the federal constitution by state governments, a series of Native Title Tribunals have been established to reconcile property rights between indigenous peoples and other interested parties, especially mining companies and white graziers.

In late 2010 and early 2011, unusually heavy rains—attributed in part to a pronounced La Niña effect in the Pacific Ocean—caused several major river systems to overrun their banks. Record flooding inundated cities and towns in the coastal region—including Rockhampton, Bundaberg, Emerald, Theodore, and St. George; the flood crisis also affected portions of New South Wales and Victoria to a somewhat lesser extent. In January the state’s premier declared three-fourths of Queensland a disaster zone; by early March, after continued heavy rains, the disaster zone had been extended to cover all but a tiny area of the state. Crops across large areas of Queensland were ruined, and key economic activities such as the mining and transport of coal were disrupted. Nearly two dozen people in Queensland died in the floods, and thousands more were displaced. Damages to infrastructure were severe; thousands of miles of road were washed out or destroyed, and it was estimated that damage to transportation infrastructure accounted for about half the monetary costs of the disaster.