Lansana was born on 22 March 1922 in Baiima, Mandu Chiefdom, Kailahun District, British Sierra Leone.

[5] Lansana was one of a small, elite group of Sierra Leoneans to be educated and trained at the Royal Military Academy Sandhurst, Berkshire, United Kingdom during the colonial period.

[3] As a Lieutenant, he was a frequent and popular visitor to the home of Sir Robert de Zouche Hall, Governor of Sierra Leone from 1952 to 1956.

On 21 March 1967, Lansana instructed Samuel Hinga Norman to conduct the extrajudicial arrest of the new, democratically elected prime minister Siaka Stevens.

[4][10] Lansana then seized control of Government House as well as the national radio and television channels and declared martial law in Sierra Leone.

[11][12] Lansana's unilateral decision was unpopular with many of his fellow Mende officers who did not believe the army should be a tool of internal government.

[4] Subsequently, Lt.-Colonel Andrew Juxon-Smith, of the Krio community, who was abroad when the coup took place, was asked to return and head the NRC military regime in 1968.

[4] Both Lansana and his sister-in-law Paramount Chief Ella Koblo Gulama were arrested on charges of treason and detained at Padema Road Prison.

[citation needed] She reportedly advised him not to stand down from the office of prime minister in spite of the APC victory.

[5] She was also reported to have offered him her formidable support and suggested that both Margai bribe Lansana to stage a coup d'état.