The federal government of Nigeria is composed of three distinct arms: the executive, the legislative, and the judicial, whose powers are vested and bestowed upon by the Constitution of the Federal Republic of Nigeria. One of the primary functions of the constitution is that it provides for separation and balance of powers among the three branches and aims to prevent the repetition of past mistakes made by the government. Other functions of the constitution include a division of power between the federal government and the states, and protection of various individual liberties of the nation's citizens.

Nigerian politics take place within a framework of a federal and presidential republic and a representative democracy, in which the president holds executive power. Legislative power is held by the federal government and the two chambers of the legislature: the House of Representatives and the Senate. The legislative arm of Nigeria is responsible for and possesses powers to legislate laws. Together, the two chambers form the law-making body in Nigeria, called the National Assembly, which serves as a check on the executive arm of government. The National Assembly of Nigeria (NASS) is the democratically elected body that represents the interests of the Federal Republic of Nigeria and its people, makes laws for Nigeria, and holds the Government of Nigeria to account. The National Assembly (NASS) is the nation's highest legislature, whose power to make laws is summarized in chapter one, section four of the 1999 Nigerian Constitution. Sections 47–49 of the 1999 Constitution state, among other things, that "There shall be a National Assembly (NASS) for the federation which shall consist of two chambers: the Senate and the House of Representatives." The Economist Intelligence Unit rated Nigeria a "hybrid regime" in 2019. The federal government, state, and local governments of Nigeria aim to work cooperatively to govern the nation and its people. Nigeria became a member of the British Commonwealth upon its independence from British colonial rule on 1 October 1960.

The law of Nigeria is based on the rule of law, the independence of the judiciary, and British common law (due to the long history of British colonial influence). The common law in the legal system is similar to common-law systems used in England and Wales and other Commonwealth countries. The constitutional framework for the legal system is provided by the Constitution of Nigeria.

The major influences on Nigeria's legal system are:

The two fundamental sources of Nigerian law through legislation are:

(1) Acts of British parliament, popularly referred to as statutes of general application during the period before independence.

(2) Local legislation (comprising enactments of the Nigerian legislatures from colonial period to date). There were other sources which, though subsumed in Nigerian legislations, were distinctly imported into the Nigerian legal systems. They are called the criminal and penal codes of Nigeria.

Nigerian legislation may be classified as follows: The colonial era until 1960, post-independence legislation 1960–1966, the military era 1966–1999.