Mai-Bornu began his civil service career at post as Administrative Officer with the Northern Nigeria Public Service, serving in the Public Service Commission and Ministry of Finance and Trade. When the Central Bank started operations in 1959, he was appointed second to the Central Bank of Nigeria as an Assistant Secretary. Subsequently he rapidly rose through the ranks from assistant secretary to deputy secretary, then secretary. He became the first indigenous Nigerian to be appointed Deputy Governor. On July 25, 1963, Mai-Bornu was appointed Governor of the Central Bank (1963–1967). After leaving the bank, he was appointed Director and General Manager of the Nigerian Tobacco Company (1967–1969). He served on the Board of Directors of the company until his death on the 23rd of February, 1970.