John Dolmayan was born in Beirut, Lebanon. During the Lebanese Civil War, the young Dolmayan's (empty) bed was hit by a stray bullet. After the incident his family decided to immigrate, and, after briefly living in Toronto, they moved to California.

Dolmayan first became interested in drums at the age of two. His father was a saxophone player and when his mother would take him to watch his father play, he would mimic his father's drummer. He learned to play the drums by putting on records and practicing, "4-6 hours a day, depending on the particular day. I did that for years and years. I developed my own style from basically taking from so many different styles. I used to play with whatever I could get my hands on, which included my Dad’s collection of jazz albums and the rock albums that my friends and I had."

Dolmayan is a fan of The Who and cites Who drummer Keith Moon as his biggest influence. Other drummers that he cites as major influences include Led Zeppelin's John Bonham, Stewart Copeland from The Police, and Rush's Neil Peart. He has also been influenced by jazz music.

Dolmayan joined System of a Down in 1997 after their original drummer, Ontronik "Andy" Khachaturian, left the band after a hand injury.

Dolmayan recorded five albums with System of a Down: System of a Down (1998), Toxicity (2001), Steal This Album! (2002), and, most recently, Mezmerize (2005), and Hypnotize (2005).

Dolmayan won DRUM! Magazine's 2006 Drummer of the year and was the feature story in their September edition.[when?]

After System of a Down's went on hiatus in 2006 Dolmayan teamed up with Daron Malakian (System of a Down's guitarist/vocalist) to form a new band called Scars on Broadway, which recorded their eponymous debut album in 2007 and 2008. The album was released in the summer of 2008 and Dolmayan, Malakian, guitarist Franky Perez, bassist Dominic Cifarelli, and keyboardist Danny Shamoun performed concerts and prepared to embark on a tour in support of the album before Malakian suddenly cancelled the tour in October of 2008.

In August 2009, Dolmayan, Franky Perez, Danny Shamoun, and Dominic Cifarelli as Scars on Broadway traveled to Iraq for a USO tour across the U.S. army bases. Their setlist consisted of covers as well as a few Scars on Broadway songs.

Scars on Broadway reunited with Malakian on May 2, 2010 and plans on doing another show in Los Angeles in August of 2010.

Dolmayan recorded drums for Killing Joke's 2003 self-titled album[citation needed], (although the band ended up going with Dave Grohl's tracks) as well as Scum of the Earth's debut album, Blah...Blah...Blah...Love Songs for the New Millennium. He also played drums on the Axis of Justice concert tour with various artists, on the Serj Tankian solo debut, Elect the Dead[citation needed], and joined Tool on stage for a few shows.[citation needed]