After playing guitar in several rock groups, Thayer formed a band with Jaime St. James. The band was originally named Movie Star, which morphed into the band Black 'n Blue in late 1981. By that time, St. James had given up his drumsticks for a microphone, and he became the lead singer of Black 'n Blue. Jeff "Woop" Warner on guitar, Patrick Young on bass, and Pete Holmes on drums rounded out Black 'n Blue's lineup.
After Geffen dropped the band, Thayer quit Black 'n Blue. Thayer and St. James were later reunited in a Kiss tribute band called Cold Gin, with Thayer playing Ace Frehley, and St. James playing Peter Criss. The band didn't go unnoticed by Kiss themselves, and they were invited to play at Kiss rhythm guitarist Paul Stanley's birthday party. Consequently, Gene Simmons, co-founder and the bassist of Kiss, offered Thayer a job as the band's personal assistant; Thayer immediately seized the opportunity. Thayer was an all-around gofer for Simmons, sometimes making coffee, sometimes traveling the country securing hotel venues for Kiss' Convention tours in the mid-1990s, and even painting Paul Stanley's house and cleaning Simmons' gutters.
When Ace Frehley left Kiss in 2002, Thayer was the band's choice to replace Frehley. Simmons and Stanley wanted to retain the classic look of the original lineup and chose Thayer to don Frehley's "Spaceman" makeup and replicate his performance antics. In March 2002, Thayer played his first show as a member of Kiss at a private function in Jamaica. The next month, he appeared at the 50th anniversary show of Dick Clark's American Bandstand, again in the Spaceman makeup. Since then, Thayer has played for Kiss in the Kiss Symphony show at Melbourne, Australia, on a mini tour of Japan, on tour with Aerosmith, on the Rock The Nation World Tour, and in several other single shows. He also played lead guitar for Kiss on their Alive/35 North American tour, which began on September 25, 2009 at Cobo Center in Detroit, MI.
Thayer has also been involved in the production of various video and CD products related to Kiss including the Kiss Symphony: Alive IV DVD, the Second Coming DVD, KissOlogy, and the main title sequence for the film "Detroit Rock City".
Thayer was elected to the board of trustees of Forest Grove, Oregon's Pacific University in 2005. Since 2007, Thayer has hosted the annual Pacific University Legends Golf Classic, an annual golf tournament held in Aloha, Oregon (near Portland) which raises money for Pacific University Athletics.
Black 'n Blue played one reunion show on December 8, 2007. The concert was a benefit for a crew member of the band, Kenny Nordone, to help pay for his medical bills, incurred whilst struggling with cancer.
On March 16, 2008, Thayer sang the Ace Frehley classic "Shock Me" for the first time on the opening night of the Kiss Alive/35 World Tour in Melbourne.
He is married to Amber Peek.
His father is a retired Brigadier General.