A coup d'état by the Lithuanian military replaced the democratically elected President Kazys Grinius with Antanas Smetona.

The 1926 Lithuanian coup d'état was a military coup d'état in Lithuania that replaced the democratically elected government with a authoritarian 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.

The Lithuanian Armed Forces are the military of Lithuania. The Lithuanian Armed Forces consist of the Lithuanian Land Forces, the Lithuanian Navy, the Lithuanian Air Force and the Lithuanian Special Operations Force. In wartime, the Lithuanian State Border Guard Service becomes part of the Lithuanian Armed Forces.

Kazys Grinius was the third President of Lithuania, holding the office from 7 June 1926 to 17 December 1926. Previously, he had served as the fifth Prime Minister of Lithuania, from 19 June 1920 until his resignation on 18 January 1922. He was posthumously awarded the Lithuanian Life Saving Cross for saving people during the Holocaust and was recognised as a Righteous Among the Nations in 2016.

Antanas Smetona was a Lithuanian intellectual, journalist and politician. He served as the first president of Lithuania from 1919 to 1920 and later as the authoritarian head of state from 1926 until the Soviet occupation of Lithuania in 1940. Referred to as the "Leader of the Nation" during his presidency, Smetona is recognised as one of the most important Lithuanian political figures between World War I and World War II, and a prominent ideologist of Lithuanian nationalism and the movement for national revival.