The Polish coup d'état attempt in Lithuania refers to a failed attempt by Polish Chief of State Józef Piłsudski to overthrow the existing Lithuanian government of Prime Minister Mykolas Sleževičius, and install a pro-Polish cabinet that would agree to a union with Poland.

Both Poland and Lithuania regained their independence in the aftermath of World War I, but both soon became engaged in territorial disputes over the Suwałki and Vilnius Regions.

Poland's Chief of State Józef Piłsudski sought a union with Lithuania in hopes of reviving the old Polish–Lithuanian Commonwealth (see Międzymorze federation).

[4] Faced with pressure from the Entente, Polish Chief of State Józef Piłsudski, who was significantly involved in planning of the coup, did not want open Polish–Lithuanian hostilities, which could lead to much bloodshed and even greater tensions between Poland and Lithuania.

[5] Instead, since he thought there were enough Polish sympathizers in Lithuania to stage a coup d'état, he decided to plan one to topple the Lithuanian government.

[7] At the time Poland signed a ceasefire in the Polish–Ukrainian War; Lithuania was invaded by the Bermontians from the north[7] and the Saxon Volunteers were leaving the Lithuanian Army.

[7] On 3 August, Wasilewski arrived at Kaunas, the temporary capital of Lithuania, to negotiate with Prime Minister Mykolas Sleževičius.

The Polish mission declared that Poland had no plans to annex Lithuania and proposed a plebiscite in the contested territories, allowing local inhabitants to determine their future.

The negotiations were then used to evaluate viability of the coup, the preparedness of the PMO, and the attitude of Lithuanian diplomats towards a union with Poland.

[16] This information was in line with the Polish plans to present the coup as an initiative by the local population to free Lithuania from German domination.

"[19] The PMO recruited Lithuanian activists Stanisław Narutowicz, Juozas Gabrys, Jurgis Aukštuolaitis, and Klemensas Vaitiekūnas.

[21] During the coup, scheduled for the night from 28 to 29 August,[21] the rebels were to capture Kaunas and hold it until the arrival of the Polish regular units invited to protect the city.

[23] Other posts were reserved for Mykolas Biržiška, Jonas Vileišis, Steponas Kairys, Juozas Tūbelis and others, similarly unaware of the coup.

Piłsudski failed to discourage local PMO activists from carrying out the Sejny Uprising in the Suwałki Region.

[29] Afraid that PMO members infiltrated the military, they secretly decided to begin mass arrests of Polish supporters on the night from 28 to 29 August.

Several dozen Poles were arrested the first night, including Aukštuolaitis and 23 Polish officers serving in the Lithuanian Army.

[35] Six leaders received life sentences (Rajmund Kowalec codename Adam Jóźwik, Jonas Niekrašas, J. Narkevičius, Vladas Kudzevičius, K. Sipavičius, and J.

[34] General Žukauskas was removed from his post as the commander of the Lithuanian Army and had to battle the perceived friendliness to Poland for much of his further career.

Piłsudski's plan was based on false assumptions and faulty intelligence, which incorrectly indicated that the Sleževičius government was deeply unpopular, and that the general Lithuanian population was relatively friendly to Poland.