As Director and Chair of Opera Studies at NEC from 2003 to 2010, John Greer was responsible for more than a dozen mainstage productions at the Cutler Majestic Theatre and introduced an additional Jordan Hall production each year to showcase NEC singers. These have included simply staged operas as well as revues of songs by Noel Coward, Cole Porter, and Stephen Sondheim. His productions at NEC ranged from Cavalli's La Calisto to the first fully staged New England performances of Adamo's Little Women.Greer continued to serve on the faculty as a vocal coach through 2011.

Active as a conductor, accompanist, vocal coach, arranger, and composer, Greer has worked in recital with many of Canada's most talented young singers of his generation including Nancy Argenta, Tracy Dahl, Rosemarie Landry, Linda McGuire, Kevin McMillian, Mark Pedrotti, Catherine Robbin, and Michael Schade. He has also worked with renowned American singers/teachers such as Carmen Balthrop, Linda Mabbs, Carmen Pelton, Ashley Putnam, William Sharp, Carol Webber, and Delores Ziegler.

As a faculty member of the University of Toronto opera division, Greer made his conducting debut in 1983, conducting numerous operas there, including The Marriage of Figaro, Gianni Schicchi, Tchaikovsky's Iolanta, and Massenet's Le Portrait de Manon. He has also developed and conducted works for Victoria's Opera Piccola, Ottawa's Opera Lyra, The Banff School of Fine Arts, the Toronto Gilbert and Sullivan Society, Mirvish Productions, the Hamilton Opera in Ontario, and the Canadian Opera Company.

For five years, Greer was the music director of the Eastman Opera Theatre in Rochester, New York, conducting operas such as Le Nozze di Figaro, Candide, Albert Herring, Patience, and The Turn of the Screw. For ten seasons, his summers have been occupied with his duties as general manager and head of music staff for the Janiec Opera Company at the Brevard Music Center in North Carolina, conducting several works, including the world premiere of David Liptak's chamber opera The Moon Singer. In the summer of 2008, Greer joined the music staff of Glimmerglass Opera in Cooperstown, New York, as head coach and continuo player for their production of Handel's Giulio Cesare.

Greer's original compositions include ten song cycles, as well as numerous works based on Canadian folk songs. His children's opera, The Snow Queen, after Hans Christian Anderson, was written for the Canadian Children's Opera Chorus and has an American premiere prior to being orchestrated by Greer and revived in Toronto leading into a European tour that included performances in Cologne and Amsterdam. His second opera is an adapatation of Oscar Wilde's fairy tale The Star-Child, with librettist Ned Dickens, and his revision and he has also orchestrated the 1889 Canadian operetta Leo the Royal Cadet by Oscar F. Telgmann, commissioned by the Toronto Operetta Theatre.

University of Manitoba and University of Southern California. Studies with Boyd McDonald, Gwendolyn Koldofsky, Brooks Smith, Malcolm Hamilton, James Fraser-Craig, Boris Goldovsky, and David Effron. Former faculty of the University of Toronto and the University of Maryland.