She was born in 1972 to Mabel and Delmar Cochran and was the third of three children. Growing up, she listened to recordings from Loretta Lynn and Barbara Mandrell. Tammy sang at her family's local church, and then she entered a talent show contest and won. She joined a couple of bands before making her own band called "TC Country" that played at fairs and weddings.
In 1998, Cochran met Shane Decker, a songwriter for Warner Bros. Records. He offered his help on making demos to send to record companies after seeing Cochran. He also helped her get a job as a songwriter for Warner Chappell. Her demo tapes were sent to Epic Records. She released her first single that same year called "If You Can", followed by "So What". Although neither single made Top 40 on the country charts, the third single ("Angels in Waiting", written about her brothers) peaked at No. 9, and its success led to the release of her self-titled debut album. The video for "Angels in Waiting" won a Christian Country Music Award for 'Video of the Year'. This album's fourth single, "I Cry", reached Top 20 as well.
Cochran's second album for Epic, Life Happened, was released a year later. The lead-off single reached Top 20, while "Love Won't Let Me", the follow-up, peaked at No. 31 and Cochran was dropped from Epic in 2003. Her third album, Where I Am, was issued on the independent Shanachie Records in 2007.
In 2014 she starred in a musical show entitled "One" at the Alabama Theatre in Myrtle Beach, South Carolina.