Upon leaving school, he joined the Sierra Leone Police Force where he served from 1923 to 1930. During this time, he rose to the rank of First Class Sergeant and Musketry Instructor.
From 1931 to 1946, he worked on the construction of the Sierra Leone Development Company (DELCO) railway, linking the Port of Pepel with the iron ore mines at Marampa. In 1943, he co-founded the ‘United Mine Workers Union’.
In 1946, he was elected to the Protectorate Assembly to represent worker interests. The following year, he took classes on ‘Labour Relations’ at Ruskin College.
In 1951, he co-founded the Sierra Leone People's Party (SLPP) and was elected to the Legislative Council. A year later, he represented SLPP in the Protectorate Assembly and became the ‘Minister of Mines, Lands and Labour’, a post he served until 1957.
In 1957, he was elected to the House of Representatives as a member for Port Loko constituency, but lost his seat as a result of an election petition the following year.
From 1958 to 1962, he served as the ‘Member of Parliament of Sierra Leone’ from Western Area Urban District.
After disagreements with the SLPP leadership, he left the party and co-founded the ‘People's National Party’ (PNP), of which he became the first Secretary-General and Deputy Leader. In 1959, when the United National Front (UNF) government was formed, he participated in the Independence Talks in London as the Deputy Leader of the PNP, which had then become part of the UNF.
After the talks, he was the only delegate who refused to sign the Independence Agreement and was thus expelled from the PNP upon his return. Then he launched the ‘Elections Before Independence Movement’ (EBIM), which later became the ‘All People’s Congress’ (APC) Party.
In the 1962 general elections, his party became the main opposition party, winning 16 seats, and he returned to parliament as member of Freetown West II. From 1962 to 1966, he served as the Mayor of the Freetown.
In the 1967 general elections, APC won by an extremely narrow margin, and he became the third Prime Minister of Sierra Leone. But within minutes of taking office, he was arrested during a military coup.After a brief period of military rule, he reassumed the post of Prime Minister in 1968.
In April 1971, a republican constitution was introduced and was ratified by the House of Representatives. On April 21, 1971, he became the first President of the Republic of Sierra Leone, with wide executive and legislative powers.
In 1973, the first general elections under the Republican Constitution were held which were marked by violence and political intimidation. As a result, the opposition party, SLPP, withdrew its nomination and gave the APC all the 85 seats in the House of Representatives.
In 1976, he was re-elected as the President without any opposition.In 1978, two years after being re-elected for a five-year term, he was sworn in for an additional term of seven years. The same year also marked the introduction of a one party constitution, and the end of opposition parties in Sierra Leone.
On November 28, 1985, he retired from office at the end of his term.