Mustafa Kemal developed his career as an Ottoman army officer, serving in conflicts before the First World War and gaining distinction at Gallipoli in 1915. His command helped resist Allied landings, and subsequent service brought further military responsibility. After the Ottoman defeat, occupation and plans to divide former imperial territory created a new political crisis. Arriving at Samsun in May 1919 on an official assignment, he instead helped organize a nationalist movement opposed to the settlement being imposed on Anatolia.

Congress meetings and the creation of a Grand National Assembly in Ankara established an alternative center of authority. Mustafa Kemal led the struggle against rival forces and invading armies, becoming commander in chief during the decisive phase of the war with Greece. Victory at Sakarya in 1921 and the offensive of 1922 brought major military success. The sultanate was abolished in 1922, and the Treaty of Lausanne in 1923 secured international recognition of the new state. The accompanying compulsory exchange of Greek and Turkish populations caused extensive uprooting and suffering.

The Republic of Turkey was proclaimed in October 1923, with Mustafa Kemal as president. His government abolished the caliphate in 1924 and pursued a broad program of secularization and state-directed reform. New legal codes replaced important elements of religious law, education was reorganized, and the Latin alphabet replaced the Arabic-based Ottoman script in 1928. Women gained political rights, including national voting rights in 1934, though social and political equality remained incomplete. That year Parliament gave him the surname Atatürk.

The reforms operated within an increasingly centralized political system dominated by the Republican People's Party. Opposition movements were restricted, revolts were suppressed, and Kurdish communities faced coercive policies within the government's Turkish nationalist project. Economic policy combined efforts to encourage development with an expanding role for the state. Abroad, Atatürk generally sought security through diplomacy and recognition of the republic's position rather than restoration of the Ottoman Empire. He remained president until his death in 1938. His career established the institutions and powerful symbolic identity of modern Turkey, while assessments must consider both social and legal transformation and the authoritarian methods and exclusions used to implement it.