The Chief of Army Staff (COAS) has been the title of the professional head of the Nigerian Army since 1966. Prior to 1966, the title was General Officer Commanding, Nigerian Army (GOCNA). Since 1980, the post has been immediately subordinate to the Chief of Defence Staff, the post held by the professional head of the Nigerian Armed Forces. The position is often occupied by the most senior commissioned officer appointed by the President of Nigeria.

The Nigerian Army (NA) is the land force of the Nigerian Armed Forces. Tracing its history to British colonial forces in West Africa, it is the largest component of the armed forces. The President of Nigeria is the Commander-in-Chief of the Nigerian Army, and its professional head is the Chief of Army Staff, who is the highest ranking military officer of the Nigerian Army. It is governed by the Nigerian Army Council (NAC). The Nigerian Army is operationally and geographically divided into ten divisions, the basic field formation. The army has been involved in operations throughout the country, most especially during the Nigerian Civil War, and has undertaken major operations abroad. Nigerian Army officers have served as chiefs of defence in other countries, with Brigadier General Maxwell Khobe serving as Sierra Leone chief of staff in 1998–1999, and Nigerian officers acting as Command Officer-in-Charge of the Armed Forces of Liberia from at least 2007.