In 1958, Luis graduated from the former Christiansted High School as his class' valedictorian. Luis studied at the Interamerican University of Puerto Rico. He moved back to Saint Croix after college, where he took a position as a sixth-grade teacher at the Christiansted Public Grammar School. He also worked as a project office manager for the Department of Housing and Urban Development before serving as a in the U.S. Army.  Luis was honorable discharged from the United States Army in 1968, holding the rank of sergeant. He returned to St. Croix after his discharge, where he married his wife, the former Luz Maria Guadalupe. He took a series of positions within the civil service and private sector until his election to office in 1972. In 1968, Luis became a personnel administrative officer in the Virgin Islands Department of Health. Luis held several positions in the private sector from 1970 to 1972. He worked for Litwin Corporation as an industrial relations manager. Luis then joined Burns International as an accountant. Finally, Luis was employed as a personnel manager and comptroller at the Estate Carlton Hotel. Luis and his wife, former U.S. Virgin Islands First Lady Luz Maria Luis, had two children, Juan Francisco Luis Jr. and Carlota Amalia. Luis was elected to the 10th Legislature of the Virgin Islands, the territory's unicameral legislative body, in 1972, when he was 32 years old. He served one, two-year term as a Senator before seeking higher office in 1974. In 1974, two years after his election to the Legislature, gubernatorial candidate Cyril King persuaded Luis to join his ticket as his running mate for lieutenant governor. King had founded the Independent Citizens Movement (ICM) in the 1960s, so he and Luis ran for office as the nominees of the ICM. King and Luis were elected as governor and lieutenant governor in a gubernatorial runoff election held in November 1974, defeating the Democratic ticket of Alexander Farrelly and Ruby Rouss. Governor Cyril King died in office of stomach cancer at Knud-Hansen Memorial Hospital at 8:06 p.m. on January 2, 1978. Luis, King's lieutenant governor, was sworn into office as the Governor of the U.S. Virgin Islands ten minutes after King's death to fill the remainder of his term. On February 21, 1978, Governor Luis appointed banker Henry Millin, a Democrat, as his first lieutenant governor in an announcement broadcast on television and radio.