During his tenure, MacKay presided over the growth of OTSL's endowment from US$682,000 to $18 million, and maintained the company's record of never posting a deficit.
He also raised funds for the construction of the Sally S. Levy Opera Center, the company's first permanent administrative facility, which was completed in 2006.
In November 2007, SFO named MacKay as its third general director, succeeding Richard Gaddes and John Crosby.
In 2013, Rossini's La donna del lago received its Santa Fe premiere in a co-production with the Metropolitan Opera.
SFO presented five world premieres during MacKay's tenure, including Cold Mountain by Jennifer Higdon and Gene Scheer (2015) and The (R)evolution of Steve Jobs by Mason Bates and Mark Campbell (librettist) (2018).
In August 2017, Santa Fe Opera announced MacKay's intention to step down as its general director after the 2018 season.