Upon passing the bar in 1939, Makasiar joined the government service as an attorney with the Department of Justice. He would not leave the government service until his retirement from the Supreme Court in 1985. Makasiar rose in the ranks, beginning with a stint with the Office of the Solicitor General, then as a trial court judge beginning in 1954. He was appointed Solicitor-General and Undersecretary of the Department of Justice from 1968 to 1970, and as Secretary of Justice from May until August 1970, at which time he was appointed as Associate Justice to the Supreme Court.