Blotzer began his career as Ratt's drummer in 1982 after he was recruited by Ratt vocalist Stephen Pearcy in place of Khurt Maier (Max Havoc, Salty Dog). Blotzer, along with bassist Tom Croucier, older brother of Juan Croucier, had previously played with noted Italian/Swiss guitarist Vic Vergeat, including a tour of the U.S. behind Vergeat's 1981 solo album Down to the Bone. Blotzer helped Ratt achieve multi-platinum success by selling five consecutive platinum albums during the 1980s. Ratt is most famous for their classic glam metal album Out of the Cellar and song "Round and Round".
At the beginning of the 1990s Ratt's popularity waned as grunge bands such as Nirvana and Pearl Jam came into the mainstream and pop metal bands were no longer in vogue. Ratt called it quits in 1992, and Blotzer started a more normal life outside the public eye.
Five years later Ratt reformed and toured once again. In 2000 Stephen Pearcy apparently quit the group, and shortly thereafter Bobby had exhibited an extreme dislike for Pearcy, who had sued the band for continuing under the "Ratt" name and claimed the band ruined their worldwide deal with Sony. Blotzer heavily denied the claims and said they were a bunch of "pathologic lies", adding that Pearcy was a "sick person". Blotzer and Ratt guitarist Warren DeMartini subsequently won the court case to use the "Ratt" name.
In 2002 former Ratt guitarist Robbin Crosby lost his battle with AIDS, which marked one of the most painful parts of Blotzer's life. Blotzer posted a message to his late bandmate affectionately referred to as "The King" by fans on the group's official web site and called Crosby "one of the most kind hearted, the most compassionate, intelligent, talented" people he had ever known. In 2007 Stephen Pearcy reunited with the group, thus putting an end to the tensions between the two. In 2009 Metal Sludge reported that he was arrested and booked on charges of domestic violence.
In 2010 Blotzer released an auto-biographical book called Tales of A Ratt - Things You Shouldn't Know.
On September 2, 2012 it was announced Bobby would be joining Geoff Tate's lineup formed after his dismissal from Queensrÿche, but he left on January 25, 2013 to return playing with Ratt.
He has played with several side projects over the years, such as Twenty 4 Seven, Phucket, FireFoxx, Airborne, Angel City Outlaws, Contraband, Vic Vergat Band, and has also played as a touring drummer for Montrose. In 2008, Blotzer, Jani Lane (Warrant), Keri Kelli (Alice Cooper), and Robbie Crane (Ratt) released Saints of the Underground's debut album, Love The Sin, Hate The Sinner.