Mac practices business and corporate law representing companies in diverse fields including biotechnology, high-tech, education, energy, and manufacturing. He assists entrepreneurs in preparing appropriate organizational structures, managing federal and state securities issues, negotiating investment terms and conditions for financings, and drafting contracts associated with the businesses.

Mac serves as Secretary and on the Boards of a number of privately-held companies and has been active in numerous nonprofit organizations in the Charlottesville area.  He is currently on the Board of the Virginia Humanities and Charlottesville Opera and on the Audit Committee of the Boys and Girls Club of Central Virginia.