Groban worked for Foster as a rehearsal singer on a series of high-profile events, including the inauguration of Grey Davis as governor of California and the Grammy Awards (at which he rehearsed Foster's "The Prayer" with Celine Dion in place of Andrea Bocelli).

He was accepted into the theater department of Carnegie Mellon University, but put his education on hold when he was offered a recording contract at Warner Bros. Records through Foster's 143 imprint. He made his recording debut singing "For Always" with Lara Fabian on the soundtrack to A.I.: Artificial Intelligence, and appeared in the 2001 season finale of the television series Ally McBeal.

His debut album, Josh Groban, was released in November 2001. Over the next year, Groban became a star. His album went double platinum, and he had his own PBS special in November 2002. A month later, he performed "To Where You Are" and "The Prayer" at the Nobel Peace Prize Concert in Oslo, Norway, and joined the Corrs, Ronan Keating, Sting, Lionel Richie, and others for a holiday performance at the Vatican in Rome.

 In November 2003, Groban issued his second album, Closer. Two months later, he earned his first number one record when Closer skyrocketed from number 11 to the top spot on the Billboard album charts. In 2006, Groban released his third studio album, Awake, featuring guest appearances by the vocal group Ladysmith Black Mambazo and jazz pianist Herbie Hancock. The holiday-themed Noel followed in 2007.