The Free Republic of the Congo (French: République Libre du Congo), often referred to as Congo-Stanleyville, was a short-lived rival government to the Republic of the Congo (Congo-Léopoldville) based in the eastern Congo and led by Antoine Gizenga.

Following Prime Minister Patrice Lumumba's deposition in September 1960 in the midst of the Congo Crisis, many of his supporters became disillusioned with the government in Léopoldville (modern-day Kinshasa). Under Lumumba's deputy, Antoine Gizenga, leftists organised in Stanleyville (modern-day Kisangani) and in December declared their own government to be the legal successor to the prime minister's administration. Gizenga quickly amassed military strength and, by February 1961, had occupied vast portions of Congolese territory. In August, negotiations between the two governments resulted in Gizenga agreeing to stand down. He returned to the office of deputy under the new prime minister, Cyrille Adoula. Still, Gizenga distanced himself from the central administration and rebuilt his own political and military power. The rival government was not fully reintegrated into the Republic of the Congo until Gizenga was arrested in January 1962.

On 30 June 1960, the Belgian Congo became independent as the Republic of the Congo. However, the domestic situation quickly devolved as the army mutinied, beginning the Congo Crisis. In spite of Prime Minister Patrice Lumumba's efforts to calm the troops, the situation worsened. Katanga and South Kasai subsequently seceded from the central government. The United Nations (UN) organised a peacekeeping operation and sent troops to the Congo. On 5 September, President Joseph Kasa-Vubu dismissed Lumumba from his post. The government was paralyzed by the political battle that ensued, and on 14 September, Colonel Joseph-Désiré Mobutu announced a takeover in Léopoldville (modern-day Kinshasa) and the installation of his own administration. Two days later, Lumumba was placed under house arrest. By October, supporters of the prime minister were convinced that few of their goals could be achieved through the new government.

Antoine Gizenga, Lumumba's deputy prime minister, left for Stanleyville (modern-day Kisangani) on 13 November to form his own government. Other nationalists attempted to join him, including Joseph Mbuyi, Maurice Mpolo, Anicet Kashamura, Christophe Gbenye, Pierre Mulele (former ministers in Lumumba's government), Joseph Okito (vice president of the Senate), and Barthélemy Mujanay (governor of the Central Bank of the Congo). Of these, only Kashamura, Gbenye, and Mulele succeeded. Mpolo and Okito were arrested and brought back to the capital while Mbuyi and Mujanay were killed in the Charlesville region.

General Victor Lundula, Lumumba's army commander who had been arrested by Mobutu, escaped custody in Léopoldville and made his way to Stanleyville. He and troops loyal to him pledged allegiance to Gizenga. Gizenga's military strength in Orientale Province rapidly increased, and his army amassed to be 6,000-strong. On 26 November Lundula organised a military parade in Stanleyville involving almost all of the military units in Orientale. The army's cohesion was primarily due to the soldiers' admiration and respect for Lundula and their attraction to Lumumba's nationalist ideals.

Also in November, the United Nations General Assembly voted to recognise a delegation assembled by Kasa-Vubu and Mobutu, definitively ending Lumumba's hopes of a legal return to power. On 27 November, the deposed prime minister escaped from his house and made his way towards Stanleyville to join Gizenga, but he was arrested five days later and imprisoned at the army camp in Thysville. Thomas Kanza, Lumumba's appointed delegate to the United Nations, switched allegiances and acted as a representative for Gizenga abroad.

On 12 December 1960, Gizenga declared his new government, the Free Republic of the Congo, based in Orientale Province, the legitimate ruling authority in the Congo. The central government almost immediately imposed an effective supply blockade along the Congo River. Despite the military power it possessed, the Stanleyville government never established an extensive administrative structure, functioning in the manner of a government in exile. Still, it had more popular support than either the College of Commissioners-General or Tshombe's government. Most administrative functions remained the responsibility of the former provincial government, which had difficulties coexisting with Gizenga's new centralised authority. The moderate deputies of the provincial assembly fled to Léopoldville.

By 20 February 1961, the Free Republic of the Congo was recognised as the legitimate government of the country by the Soviet Union, China, Mongolia, Poland, East Germany, Yugoslavia, Albania, Bulgaria, Hungary, Cuba, Iraq, the United Arab Republic, Ghana, Guinea, the Algerian provisional government, and Morocco. Gizenga demanded that Western nations relocate their embassies to Stanleyville or risk having their consuls expelled.