Said Wilbert Musa was born in San Ignacio on 19 March 1944, the son of Belizean Aurora Gibbs and Palestinian immigrant Hamid Musa. After attending primary and secondary school in Belize, he went to Manchester, England, where he received a law degree from Manchester University in 1967. He married the former Joan Pearson in 1967.
Musa returned to Belize in the late 1960s, serving as Circuit Magistrate (1967–68) and Crown Counsel (1968–70), before going into private law practice, setting up the law firm of Musa and Baldermos in 1970. He also became involved with the United Black Association for Development (UBAD) and was co-founder of the People's Action Committee (PAC) and the Society for the Promotion of Education and Research (SPEAR). PAC, with UBAD, eschewed party politics in favor of popular organization. But after the PAC/UBAD alliance broke up, Musa joined the PUP, making an unsuccessful bid for Parliament in 1974. By joining the PUP, he believed he could be more effective in what he considered the country's major challenge, increasing popular participation in government and political life.