Manuel de Arriaga, a prominent lawyer and politician, was elected as the first President of Portugal after the establishment of the Portuguese Republic. This pivotal moment occurred following the Republican revolution in 1910, which resulted in the deposition of the monarchy and a significant shift in the governance of Portugal. Arriaga was elected by the National Assembly, and his presidency commenced amid widespread hopes for reform and modernization in a country that had long been under royal rule. His swearing-in took place on August 24, 1911, in Lisbon, symbolizing a break from centuries of monarchy and a shift towards a democratic framework.

Arriaga aimed to stabilize the republic by addressing pressing social issues and uniting various political factions. His presidency was not without challenges; he faced opposition from both monarchy supporters and radical republicans who demanded more profound changes. The political atmosphere was charged, as the new republic struggled to define its identity amidst internal divisions and external pressures. Despite his initial popularity, Arriaga's tenure saw difficulties, including coalition politics and societal unrest, which ultimately led to his resignation in 1915.

The election and inauguration of Arriaga marked the founding of a new constitutional framework designed to foster democracy in Portugal. His leadership was crucial in navigating the complexities of a newly established republic, serving as a key transitional figure in the years before World War I. The changes initiated during this time laid the groundwork for future political developments in Portugal, eventually influencing the country's direction and governance for decades to come.