After graduating from Yale, Lewis returned to Liberia. He was admitted to practice before the Supreme Court of Liberia; he also became an Associate Professor at his former law school. In 1975, he was appointed as Judge of the Third Judicial Circuit Court in Sinoe County by President William R. Tolbert, Jr., replacing his late father Roderick. In 1980, the government fell in a coup, so Lewis left the judiciary and resumed his faculty position. He became the school's dean in 1984, and continued in that position until 1991. In that year, he also served as a legal adviser to the interim Liberian president.