Nigerian politics takes place within a framework of a federal, presidential, representative democratic republic, in which executive power is exercised by the government. The legislative power is held by the real government and the two chambers of the legislature: the House of Representatives and the Senate. Together, the two chambers make up the law-making body in Nigeria, called the National Assembly, which serves as a check on the executive arm of government. The highest judiciary arm of government in Nigeria is the Supreme Court of Nigeria which was created after independence. The following are some of the roles of the legislative arm of government in Nigeria;

1. Legislative or Law-Making Functions:

The first main function of a legislature is to legislate i.e. to make laws. In Nigeria's contemporary era of democracy, legislature is the chief source of law. It is the legislature which formulates the will of the state into laws and gives it a legal character. Legislature transforms the demands of the people into authoritative laws/statutes.

2. Deliberative Functions:

One of the important roles of the legislature is to  deliberate upon matters of national importance, public issues, problems and needs. Through this function, the legislature reflects the public opinion over various issues. The debates held in the legislature have a great educative value for the people.

3. Custodian of National Finances:

A near universal rule is that “the legislature of the state is the custodian of the national purse.” It holds the purse of the nation and controls the finances. No money can be raised or spent by the executive without the approval of the legislature. Each year the executive has to prepare and get passed from the legislature the budget for the coming financial year. In the budget, the executive has to place the account of the actual income and expenditure of the previous year and estimated income and expenditure for the New Year.

Not only the legislature passes the budget but also it alone can approve the imposition, or repeal or collection of any tax whatsoever. Further, the legislature maintains a control over all financial transactions and expenditures incurred by the executive.

4. Control over the Executive:

A modern legislature has the power to exercise control over the executive. In a Presidential form of government, like the one which is at work  in Nigeria currently, the legislature exercises some checks over the executive. It can appoint investigation committees to probe the functioning of government departments. By the use of its power to legislate and pass the budget, the legislature exercises a fair amount of control over the executive. 

5. Constituent Functions:

In almost every state in many countries, it is the legislature which has the power to amend the constitution. For this purpose, the legislature has to pass special laws, called amendments, in accordance with the procedure laid down in the Constitution. In some states, the requirement is that the legislature must pass the amendment with two-thirds or three-fourths or an absolute majority of votes.

6. Oversight Functions:

The Legislature’s oversight powers are contained in Sections 82-89 of the Nigerian constitution with regard to the National Assembly, and 120-128 with regard to the state Houses of Assembly, i.e. supervising the other arms of government to ensure that they implement government policies and programmes as contained in the Nigerian Annual Appropriation Act/Law of Government.

7. Judicial Functions:

It is conventional to give some judicial power to the legislature. Usually, the legislature is assigned to act as a court of impeachment i.e. as an investigating court for trying high public officials on charges of treason and high crimes and remove them from office. It also has the power to pass a resolution for the removal of Judges of the Supreme Court and of the High Court’s on the ground of misbehavior or incapacity.