In 1901, Western Australia became the last of the Australian colonies to join the Federation, after securing several key concessions, including the promise of a transcontinental railway connecting Perth to the eastern states. This marked the beginning of Perth’s integration into the newly-formed Commonwealth of Australia, and its journey into modernity. However, it wasn’t until 1927 that a deeply troubling racial policy was enforced, which banned Indigenous people from entering much of Perth under threat of imprisonment—this restriction persisted until 1954.

In 1933, a significant political event shook the state when two-thirds of Western Australians voted in favor of secession from the Federation. However, the political tide turned when voters elected a government opposed to secession. Despite their opposition, the new government submitted the issue to the Imperial Parliament, but after 18 months of deliberation, the request for secession was ultimately rejected, and Perth remained firmly part of Australia.

Post-World War II, Perth was entering an era of transformation. With a population of around 280,000, the state was struggling with economic stagnation. But by the 1940s and '50s, government initiatives, including large-scale public works, the establishment of new industries, and an influx of immigrants, paved the way for significant economic development. Key projects like the Mundaring and Wellington dams, a new Perth Airport, and the Kwinana industrial area set the stage for rapid growth.

This period also saw major infrastructure changes, including the expansion of the city’s highway network, encouraged by the Stephenson-Hepburn Report. The Narrows Bridge, completed in 1959, and the eventual closure of the Perth-Fremantle Tramways symbolized the city's shift towards more modern, car-oriented development. The 1960s mining boom further spurred this growth, cementing Perth's role as the service center for the state's lucrative resource industries, including gold, iron ore, and natural gas.

In 1962, Perth gained international attention when its residents lit their house and street lights to mark American astronaut John Glenn's orbit, earning the city the nickname "City of Light." The gesture was repeated in 1998 when Glenn passed overhead again during a space shuttle mission.

By the 1990s, Perth had firmly established itself as a prosperous urban hub, driven by its role in servicing Western Australia's vast resource industries. In 1994, the state government created the City of Perth, separating it from the surrounding suburban districts and solidifying its status as a modern metropolis. Today, Perth remains a vibrant and growing city, reflecting a rich history of change, challenges, and successes.