The 20th century in Queensland was a period of profound change, marked by both progress and challenges. One of the landmark moments came in 1905 when women were granted the right to vote in state elections, a significant step forward for women's rights in Australia. The following years saw the establishment of key institutions, including the University of Queensland in 1909, which played a pivotal role in shaping the state's educational landscape. Additionally, Queensland pioneered some of the first alternative treatments for polio in 1911, which are still used globally today.

World War I had a lasting impact on Queensland, with more than 58,000 Queenslanders serving in the conflict and over 10,000 losing their lives. The effects of the war were felt deeply across the state, marking a somber chapter in its history. Meanwhile, in 1920, Queensland gave birth to Australia's first major airline, Qantas, originally founded in Winton under the name "Queensland and Northern Territory Aerial Services," which began connecting remote areas of the state and nation.

In 1922, Queensland became the only Australian state to adopt a unicameral parliament, abolishing its Legislative Council, a move that reshaped the state's governance. However, not all changes were beneficial. In 1935, the introduction of cane toads from Hawaii in an attempt to control cane beetles backfired, leading to an ongoing environmental issue. By 1962, Queensland had become the site of the first commercial oil production in Australia, a milestone that contributed to the state's economic diversification.

World War II further shaped Queensland’s role on the global stage. Brisbane became the center for Allied operations in the Pacific, housing the headquarters of General Douglas MacArthur, the chief of Allied Pacific forces. Tensions between US military personnel and Australian servicemen led to the infamous Battle of Brisbane in 1942, highlighting the strain of wartime alliances. Following the war, Queensland saw a significant influx of immigrants, particularly from Southern and Eastern Europe, which enriched the state’s cultural fabric.

The later decades of the 20th century saw Queensland benefit from its subtropical climate, with air conditioning making it an increasingly popular destination for interstate migrants. In 1966, U.S. President Lyndon B. Johnson’s visit to Queensland underscored the growing international significance of the state. The end of the White Australia policy in 1973 ushered in a new era of immigration from Asia, contributing to the state's growing multicultural identity. In 1981, Queensland's natural beauty was internationally recognized when the Great Barrier Reef was declared a UNESCO World Heritage Site.

As the century drew to a close, Queensland continued to experience growth and development, despite challenges such as the major floods of 2010-2011 and the global COVID-19 pandemic in 2020, which prompted widespread social distancing and border closures. These events, along with the state's rapid population growth, ensured that Queensland's 20th-century legacy would be one of both resilience and transformation, positioning it as a dynamic and diverse state within Australia.