Shortly after his return from studies in Australia, Taufa'ahau was appointed to the Cabinet as the Minister of Education. A year and a half later, the portfolio of Minister of Health was added to his duties. He held these two portfolios until December 1949, when he became Premier of the Kingdom, combined with the portfolios of Education, Agriculture, and Foreign Affairs. In 1962, the portfolio of Works was added to his many duties.
During the 16 years that the crown prince served as premier, Tonga underwent a number of important economic and social changes. One of his earliest aims was to improve the standard of education in the kingdom, and he was the moving force behind the establishment of Tonga's Teacher Training College and Tonga High School. As a result, Tonga has one of the highest literacy rates in the Pacific Basin region.
Taufa'ahau was also instrumental in developing Tonga's agricultural sector via the establishment of a number of boards and councils whose duties were to facilitate the handling and marketing of Tongan produce locally and regionally. The Tongan Broadcasting Commission, the International Dateline Hotel, Queen Salote Wharf and the government newspaper, the Tongan Chronicle, were all established under the Crown Prince's leadership. Because of these many achievements, the British accorded him a Commander of the Order of the British Empire and a Knight of the British Empire in 1951 and 1958, respectively.
In 1965, Her Highness Queen Salote Tupou III died. Two years later, on 4 July 1967, after a year of mourning and another year of preparation, Crown Prince Taufa'ahau Tupou IV was crowned King of Tonga in the Royal Chapel in Nuku'alofa, the capital of Tonga.