Muammar Gaddafi became the de facto leader of Libya on 1 September 1969 after leading a group of Libyan Army officers against King Idris I in a bloodless coup d'état. When Idris was in Turkey for medical treatment, the Revolutionary Command Council (RCC) headed by Gaddafi abolished the monarchy and the constitution and established the Libyan Arab Republic, with the motto "Unity, Freedom, Socialism". The name of Libya was changed several times during Gaddafi's tenure as leader. From 1969 to 1977, the name was the Libyan Arab Republic. In 1977, the name was changed to Socialist People's Libyan Arab Jamahiriya. Jamahiriya was a term coined by Gaddafi, usually translated as "state of the masses". The country was renamed again in 1986 as the Great Socialist People's Libyan Arab Jamahiriya, after the United States bombing that year.

After coming to power, with the oil price rise of the 1970s and consequential rise of the Libyan economy, the RCC government initiated a process of directing funds toward providing education, health care and housing for all. Public education in the country became free and primary education compulsory for both sexes. However, the quality of the education system was far below many other Arab states, even those with much less oil wealth, with 2 hours a week being dedicated to his Green Book. It was also illegal to learn a second language for more than a decade. There were instances of revolt, like the 1976 Libyan protests. There was some students who even faced public execution in the university, witnessed by many other students and broadcast on Libyan state television, such as the Execution of Al-Sadek Hamed Al-Shuwehdy. Medical care became available to the public at no cost, but the quality was far below those of some of its neighbours (Tunisia, Egypt & Malta) which prompted many Libyans to get medical treatments in those countries. Providing housing for all was a task the RCC government was unable to complete. Under Gaddafi, per capita income in the country rose to more than US$11,000 in nominal terms, and to over US$30,000 in PPP terms, the 5th highest in Africa. The increase in prosperity was accompanied by a foreign policy hostile to the other Arab states of the region, an anti-West foreign policy, and increased domestic political repression.

During the 1980s and 1990s, Gaddafi, openly supported foreign groups like the African National Congress, the Palestine Liberation Organization, the Provisional Irish Republican Army , Polisario Front and Moro National Liberation Front as well as warloards such as Charles Taylor, Abu Sayef, Abu Nidal and dictators across Africa such as Idi Amin, Jean-Bédel Bokassa and Mengistu Haile Mariam. In the Middle East, he formed alliances with what the US then referred to as the “Radical camp”, composed of Ba'athist Syria, Iran and South Yemen. Gaddafi's government was often suspected of participating or aiding attacks by terrorist groups. Additionally, Gaddafi undertook several invasions of neighboring states in Africa, notably Chad in the 1970s and 1980s. All of his actions led to a deterioration of Libya's foreign relations with several countries, mostly Western states and the Arab world, and culminated in the 1986 United States bombing of Libya as well as the support of Ba'athist Iraq, Egypt, Saudi Arabia, Morocco and Sudan toward’s Chad against Gaddafi. Gaddafi defended his government's actions by citing the need to support anti-imperialist and anti-colonial movements around the world. Gaddafi's behavior was often erratic and led many (from the West, as well as from the Arab world) to conclude that he was not mentally sound, a claim disputed by his regime. Despite this, his actions have often led to interrogations. François Mitterrand called him an “unstable man”, Ronald Reagan dubbed him the “mad dog of the Middle East” and for Anwar al-Sadat, he was literally a “possessed demon”. Despite receiving extensive aid and technical assistance from the Soviet Union and its allies, and aligning his country with the Eastern Bloc, Gaddafi retained ties to some pro-American governments in Western Europe, largely by courting Western oil companies with promises of access to the lucrative Libyan energy sector. After the 9/11 attacks, strained relations between Libya and NATO countries were mostly normalised, and sanctions against the country relaxed, in exchange for nuclear disarmament.

In early 2011, a civil war broke out in the context of the wider Arab Spring. The rebel anti-Gaddafi forces formed a committee named the National Transitional Council in February 2011, to act as an interim authority in the rebel-controlled areas. After killings by government forces in addition to those by the rebel forces, a multinational coalition led by NATO forces intervened in March in support of the rebels. The International Criminal Court issued an arrest warrant against Gaddafi and his entourage in June 2011. Gaddafi's government was overthrown in the wake of the fall of Tripoli to the rebel forces in August, although pockets of resistance held by forces in support of Gaddafi's government held out for another two months, especially in Gaddafi's hometown of Sirte, which he declared the new capital of Libya in September. The fall of the last remaining sites in Sirte under pro-Gaddafi control on 20 October 2011, followed by the killing of Gaddafi, marked the end of the Libyan Arab Jamahiriya.

The discovery of significant oil reserves in 1959 and the subsequent income from petroleum sales enabled the Kingdom of Libya to transition from one of the world's poorest nations to a wealthy state. Although oil drastically improved the Libyan government's finances, resentment began to build over the increased concentration of the nation's wealth in the hands of King Idris. This discontent mounted with the rise of Nasserism and Arab nationalism/socialism throughout North Africa and the Middle East.^{[citation needed]}

On 1 September 1969, a group of about 70 young army officers known as the Free Officers Movement and enlisted men mostly assigned to the Signal Corps, seized control of the government and in a stroke abolished the Libyan monarchy. The coup was launched at Benghazi, and within two hours the takeover was completed. Army units quickly rallied in support of the coup, and within a few days firmly established military control in Tripoli and throughout the country. Popular reception of the coup, especially by younger people in the urban areas, was enthusiastic. Fears of resistance in Cyrenaica and Fezzan proved unfounded. No deaths or violent incidents related to the coup were reported.

The Free Officers Movement, which claimed credit for carrying out the coup, was headed by a twelve-member directorate that designated itself the Revolutionary Command Council (RCC). This body constituted the Libyan government after the coup. In its initial proclamation on 1 September, the RCC declared the country to be a free and sovereign state called the Libyan Arab Republic, which would proceed "in the path of freedom, unity, and social justice, guaranteeing the right of equality to its citizens, and opening before them the doors of honorable work." The rule of the Turks and Italians and the "reactionary" government just overthrown were characterized as belonging to "dark ages", from which the Libyan people were called to move forward as "free brothers" to a new age of prosperity, equality, and honor.

The RCC advised diplomatic representatives in Libya that the revolutionary changes had not been directed from outside the country, that existing treaties and agreements would remain in effect, and that foreign lives and property would be protected. Diplomatic recognition of the new government came quickly from countries throughout the world. United States recognition was officially extended on 6 September.