He came to prominence in the 1980s as the lead singer and lyricist of Armored Saint, a heavy metal band from Los Angeles, California.

Bush has also been active with the reformed Armored Saint intermittently from 1999 to the present, and involved with other projects such as Metal Allegiance and Category 7.

Eduardo Rivadavia of AllMusic praised Bush's "remarkable voice"[1] while authors Howie Abrams and Sacha Jenkins ranked him as the eighth-best vocalist in the genre.

[2] Bush started his singing career at Woodrow Wilson High School (Los Angeles) in 1979, fronting a short-lived rock band called "Royal Decree", with brothers Felipe "Phil" Sandoval (lead guitar) and Gonzalo "Gonzo" Sandoval (drums), and bassist Joey Vera, also Woodrow Wilson High School alumni.

In 1982, they all became founding members of Armored Saint, along with new lead guitarist Dave Prichard, from South Pasadena High School.

In 1984, Bush had a cameo appearance in the Huey Lewis and the News video "The Heart of Rock & Roll" at the 1:38 mark (exiting from the limo).

Despite rave reviews from the metal press,[citation needed] the band decided that they did not want to continue without Prichard, and amicably disbanded.

The following year, Armored Saint released a collection of demos, live tracks and other rarities in the two-disc package Nod to the Old School.

Anthrax recorded Sound of White Noise, Stomp 442, & Volume 8: The Threat Is Real with Bush in the 90s before entering a temporary hiatus during 1999.

He was later approached again by the band to re-join following Belladonna's exit, which he again turned down, explaining: "I couldn't go back and say, 'Here I am...' It would be like coming in with my tail between my legs, and that's not right for me.

[4][5] Bush also performed with Anthrax at the Loud Park '09 Festival in Japan on October 17, 2009,[6] followed by five concerts on the Soundwave tour in Australia in February 2010.

On December 14, 2009, it was announced that the "Big Four" thrash bands would play in Poland and Czech Republic during the following year, among several other shows during the Sonisphere festival.

[10] In April 2011, German instrumental rock band Long Distance Calling released a self-titled full-length album, which features John Bush performing vocals for the track "Middleville".

[12] Bush performed vocals for the track "Bound by Silence" from Metal Allegiance's 2018 album Volume II – Power Drunk Majesty.