After receiving her law degree, Professor MacKenzie served as a law clerk to Chief Justice William S. Richardson of the Hawaiʻi Supreme Court. In 1980, she joined the staff of the Native Hawaiian Legal Corporation (NHLC), a public interest law firm protecting and advancing the rights of Native Hawaiians. She served as NHLC's Executive Director from 1982-1986 and as a senior staff attorney from 1986-1992. From 1992-1999, she was the Executive Director of the Hawaiian Claims Office, a state program established to review and make recommendations on claims by Hawaiian Home Lands beneficiaries. Professor MacKenzie has worked on cases asserting Hawaiian traditional and customary rights, dealing with land issues, and defending the constitutionality of Hawaiian programs. She currently teaches Native Hawaiian Rights, the Native Hawaiian Rights Clinic, the Second Year Seminar legal writing course, and specific topics courses in Native Hawaiian law. Prof. MacKenzie is the current President of the Native Hawaiian Bar Association, which she helped to establish in 1992. She also serves on the Board of Directors of Nāonealaʻa/Hikaʻalani, a Native Hawaiian cultural organization.