The 1926 Lithuanian coup d'état was a military coup d'état in Lithuania that replaced the democratically elected government with a nationalist regime led by Antanas Smetona. The coup took place on 17 December 1926 and was largely organized by the military; Smetona's role remains the subject of debate. The coup brought the Lithuanian Nationalist Union, the most conservative party at the time, to power. Previously it had been a fairly new and insignificant nationalistic party. By 1926, its membership reached about 2,000 and it had won only three seats in the parliamentary elections. The Lithuanian Christian Democratic Party, the largest party in the Seimas at the time, collaborated with the military and provided constitutional legitimacy to the coup, but accepted no major posts in the new government and withdrew in May 1927. After the military handed power over to the civilian government, it ceased playing a direct role in political life.

Mykolas Sleževičius was a Lithuanian lawyer, political and cultural figure, and journalist. One of the most influential figures in inter-war Lithuania, he served as the prime minister of Lithuania on three occasions. Taking the helm of the government at a difficult time in 1918 and again in 1919, Sleževičius has been credited with preparing Lithuania for the fights to come and for laying the foundations of the fledgling state.