Dia attended the École normale supérieure William Ponty in Dakar and became a teacher.
In 1948 he was elected to the French Senate, where he served until 1956. He also studied in Paris law and economics. Politically, he was active in the Union Party progressiste Sénégalaise Leopold Sedar Senghor of the later president. January 2, 1956 he was a deputy of the National Assembly in Paris. After Senegal in 1958 became autonomous, he was born on May 18, 1958 Prime Minister of the country. In the Mali Federation between Senegal and neighboring Mali, he took over after independence from France on 20 June 1960, the Office of the Vice President; the Federation broke up but after about two months.
In Senegal, he remained in office of the Prime Minister. In June 1962 he took a trip in several countries of the Eastern bloc and Senegal established diplomatic relations with the Soviet Union. Contrasts between the temperate Senghor and the more radical socialists slide escalated on 17 December 1962. To avoid a confidence vote in parliament, the parliament building was occupied on the order of slides of the army and police. The parliamentarians avoided but for the house of the President of Parliament and spoke slide with 48 of 80 votes, the vote of no confidence. Although the chief of staff assisted slide, but troops who were loyal to Senghor, occupying the broadcasting station and sat firmly and slide the trailer. The next day the Parliament Senghor authorized a new constitution with a presidential system to develop and to be confirmed in a referendum. In January, the deputies to make slide in court. He was sentenced to life imprisonment, two other former ministers, each twenty years. The President appointed a prime minister again in 1970.
His imprisonment, which he spent in Kédougou in the east of the country, ended in 1974. On January 27, 1983, he joined the presidential election against Senghor in 1981 reigning successor Abdou Diouf. He finished with 1.39% of votes in third place after the victorious Diouf and later president Abdoulaye Wade. In 1985, he published his memoirs under the title Mémoires d'un militant du Tiers Monde. In January 2002 he tried in vain to annul the judgment of 1963.