Summers grew up in Loogootee, IN, and studied at Indiana University. After graduation he worked with San Francisco's Western Opera Theater and the Merola Opera Program. He has been principal guest conductor of the San Francisco Opera since 1989. He made his premiere with Opera Australia in 1994. Summers' first performance at the Metropolitan Opera was a 1998 performance of Die Fledermaus. He became music director of Houston Grand Opera in 1998 and in 2011 was appointed to the company's newly created dual position of artistic and music director. Summers' involvement in the creation of new operas had begun at the San Francisco Opera, where he led André Previn's A Streetcar Named Desire and Jake Heggie and Terrence McNally's Dead Man Walking. In Houston he has continued to work extensively with living composers and has commissioned and premiered a number of new operas, many of which are among the most significant and popular American works of the late 20th and early 21st centuries. Works that he has been instrumental in creating include Mark Adamo's Little Women, Rachel Portman's The Little Prince, and Carlisle Floyd's Cold Sassy Tree. Tod Machover, Daniel Catán, Lee Hoiby, Michael Daugherty, and Christopher Theofanidis are among the composers with whom he has worked.
He has also led performances at Barcelona’s Gran Teatre del Liceu, Welsh National Opera, Santa Fe Opera, Opéra de Bordeaux, Rome Opera, and Lisbon Opera. Orchestras that he has led include the Boston Symphony, the Royal Concertgebouw Orchestra, the English Chamber Orchestra, the Rotterdam Philharmonic, and the Los Angeles Philharmonic.
In 2002 he received a Grammy Award for the album Bel Canto, featuring soprano Renée Fleming and the Orchestra of St. Luke's. Other recordings include Adamo's Little Women, Heggie's Dead Man Walking, Catán's Florencia en el Amazonas, and Previn's Brief Encounter, as well as DVDs of The Marriage of Figaro, La Cenerentola, I Puritani, and Madama Butterfly.