After attending The Peddie School in Hightstown, New Jersey, Niels earned his B.A. from the University of Maryland. He taught history for several years and then became the founding regional director of the Fellowship of Christians in Universities and Schools (FOCUS) in Baltimore. Niels also holds a M.T.S. from the Regent College, University of British Columbia, and a M.A. in education administration from Columbia University Teachers College.
Niels has received numerous honors and awards. In college, he was an All-American goalie and co-captain of the 1975 NCAA Championship Lacrosse Team at the University of Maryland. He received the Reginald Van Trump Truitt Award from the university for "Scholastic Achievement and Team Performance." In 1991, the annual Excellence in Teaching Award given by Saint Andrews School was renamed The Gary J. Niels Excellence in Teaching Award. In 1995, Niels was awarded the prestigious Klingenstein Fellowship by Teachers College, Columbia University. He has also received the Distinguished Alumni Service Award from the Peddie School. Niels has served on the Board of the Pennsylvania Association of Independent Schools (PAIS) and been President of the Pittsburgh Consortium of Independent Schools. He is also on the Advisory Board for Education Innovation at Hathaway Brown School. Niels has presented at numerous conferences and published many articles on different educational topics, most notably issues of academic integrity and school honor codes.Niels actively enjoys many sports, most notably biking, tennis, and skiing. He has four sons: Christopher, Billy, Brawley, and Morrow. He and his wife Elizabeth live in Highland Park.