Tembo was elected to the legislative assembly of Nyasaland in 1961, three years before the country gained its independence and became the Republic of Malawi. He was the second Minister of Finance in Malawi after independence, succeeding Henry Phillips (later Sir Henry Phillips) in a post for which the intended candidate had been Dunduzu Chisiza (Chisiza died in 1962 in a car crash). John Tembo was the only cabinet member not to resign in the notorious Cabinet Crisis of 1964, after which most of the President's closest lieutenants, their opposition to his policies thwarted, fled the country. (Chinua Achebe in "A Man of the People" admits having used a real situation gleaned from the Hansards of a certain African country to portray his main character 'Chief Nanga', the heckler in parliament who hounded out the 'offensive minister' who had just resigned.)