Bennett was born in Clinton, New York, and attended high school at Clinton Central School. In 1967, she enrolled in Pembroke College, but graduated in 1971 from Brown University after the two schools merged.
While at Brown, Bennett concentrated her studies in the classics and intended to become a teacher. She acted in Sock and Buskin theatrical productions, was a member of a jazz band, and was a singer with the "Chattertocks" a cappella group. She performed in other groups as well, including one at the Berklee School of Music.
Bennett's career began in 1974 when she was recorded as the voice of First National Bank of Atlanta's "Tillie the All-Time Teller." She has recorded messages for the public address system in all Delta Air Lines terminals worldwide, as well as voicing e-learning software and GPS navigation software, and telephone systems. Bennett's voice has also been used in numerous local and national television advertisements for Ford, Coca-Cola, Fisher-Price, McDonald's, The Home Depot, Goodyear, Visa, Macy's, Hot Pockets, Club Med, and Cartoon Network, among others.
In June 2005, the software company ScanSoft was looking for someone to be the voice for a database project involving speech construction. ScanSoft inquired with GM Voices and selected Bennett, who happened to be present when the scheduled voice-over artist was absent. She worked in a home recording booth for the entire month of July 2005, more than four hours each day, reading phrases and sentences. The recordings were then concatenated into the various words, sentences, and paragraphs used in the Siri voice. Bennett only became aware she was the voice of Siri when a friend contacted her through email in October 2011.
Despite Apple not having acknowledged or confirmed its use of Bennett, audio-forensics experts hired by CNN expressed 100 percent certainty that Bennett is the voice of Siri.
While at Brown University, Bennett met her husband, Curt Bennett, who played in the National Hockey League as well as for the United States national ice hockey team in the 1970s. Bennett now lives in Atlanta, Georgia and has a son Cameron and a pet tabby cat named Boo.
Around October 4, 2013, she appeared on CNN "New Day" explaining how she got picked to play the part of Siri.
In the March 13, 2015 episode of Adult Swim's The Jack and Triumph Show, titled "Siri", Bennett appeared as herself, and was referred to as the "voice of Siri".
In July 2016 Bennett appeared on comedian Anthony Anderson's ABC game show To Tell the Truth, and was revealed as the true voice of Siri.
Bennett voiced Batman's computer in the 2017 animated feature film The Lego Batman Movie. Bennett used her Siri voice, but was credited as Siri as a joke. As an update for the iPhone, whenever the user says 'Hey Computer' to Siri, she will respond with Batman related things.