Sir Albert played an active role in the debates over the Stevenson Constitution and was one of the chief spokesmen for protectorate interests. He also held several cabinet positions such as Education, Agriculture, Natural Resources and Finance between 1951 and 1964. In 1951, he was elected to the Legislative Council as the first Protectorate Member, and became the first Minister of Education in 1952. In 1957, he returned to Parliament after the general elections as M.P. for Moyamba South Constituency. Shortly after the elections, he challenged his elder brother Sir Milton for the leadership of the party and was elected leader of the S.L.P.P. but later stepped down for his elder brother after he had been guaranteed that his closest ally, Siaka Stevens, would return to cabinet. It was Sir Milton's failure to honour this and other pledges that led Albert to refuse the cabinet position he had been offered, and form his own party, called People's National Party, in September 1958. Sir Albert was appointed Minister of Agriculture in the United Front Coalition in 1959. In 1962, he returned as M.P. for Moyamba South Constituency and shortly after that he became Minister of Finance where he introduced the decimal currency, the "Leone" as legal tender, and established the Bank of Sierra Leone as the Central Bank . Sir Albert Margai became Prime Minister on April 29, 1964, after the death of Sir Milton.
At the time he became leader of the S.L.P.P. and Head of Government, Sir Albert was no longer a young man, as he did not enjoy the reverence which old age had bestowed upon his elder brother. As first lawyer from the protectorate, he was highly respected but, unlike Sir Milton, he did not enjoy the support and confidence of all the factions within his party. As a recognised leader of the progressive wing of the S.L.P.P., he was part of those that advocated for the development of Sierra Leone and took an "African" stand on most international issues. Sir Albert also paid less attention to traditional institutions, and while he was leader of the People's National Party (PNP), he openly asked traditional rulers to stay out of politics.
As Prime Minister, Sir Albert, who had come to be popularly known as "Big Albert," "Albert of Africa," and "Akpata," infused dynamism and glamour into the somewhat sedate politics of Sierra Leone.
He had great respect and admiration for President Sekou Toure of Guinea and Kwame Nkrumah of Ghana, and sought to emulate the two leaders in their stands on international issues and their preoccupation with politicising the mass of their people. Sir Albert personified the African personality both in his attire and his public utterances on African issues.
Before the appointment of Sir Albert Margai, S.L.P.P. politics was largely a conservative affair left to chiefs, elders and opinion leaders. Sir Albert added glamour by increasing pomp and pageantry in the office of Prime Minister. Outriders on motorcycles and police landrovers with blaring sirens became more conspicuous. Gaily attired women in ashobi, young men in party t-shirts, praise singers and drummers also became a regular feature of the political scene. With the introduction of the institution of Mammy Queens, women suddenly became important in politics, organising their fellow women in sections to provide political support for the leadership.
In his attempt to project himself as a symbol of national unity and as catalyst for mobilising the progressive forces of the country, Sir Albert found himself in the same dilemma in which many African leaders of his time found themselves. His impatience with the gradualism of the older generation, and his revolt against their authority, not only alienated him from a section that still had considerable sway, but also opened him to attacks from younger elements who perceived his efforts as not going far enough.
Racked by accusations of corruption in high places and also disregard for the interests of significant sectors of the population, Sir Albert lost the 1967 elections to the opposition A.P.C., and in the process became the first and only leader of an African state to have officially lost an election.
In spite of the failings of his regime, this genial giant that threaten to shoot down his opponents, he had profound respect for the law and the constitution of the land. He relied on legal rather than extra-legal means in his fight against his opponents, and in the process helped to preserve a sacred heritage.