In the US, McGegan has served as artist-in-residence at Washington University in St. Louis, beginning in 1979, when he was initially scheduled for one semester in residence, but continued until 1985.[3] McGegan first guest-conducted the St. Louis Symphony in 1986, and has since returned continuously as a guest conductor.[4] In 1985, McGegan became music director of the Philharmonia Baroque Orchestra in San Francisco and Berkeley, California.[5] In 1988, he served as Music Director of the Ojai Music Festival alongside Peter Maxwell Davies and Diane Wittry. Since 2013, he has been Principal Guest Conductor of the Pasadena Symphony. In October 2018, the Philharmonia Baroque Orchestra announced that McGegan is to stand down as its music director after the 2019–20 season, becoming music director laureate.[6]
McGegan has made more than 100 recordings, including many with Philharmonia Baroque and singers such as Lorraine Hunt Lieberson and Lisa Saffer, for such labels as Philharmonia Baroque Productions and harmonia mundi.[9] In 2023, he conducted Cantata Collective's performance of Bach's St John Passion for Avie Records.[10]