Mortal Sin is an Australian thrash metal band that formed in 1985.

As arguably the first band in Australia to play purely thrash metal, Mortal Sin quickly developed a solid following and only seven months after their first live show the band recorded an album-length demo in a mere three days in July 1986. The eight track recording was eventually released in late 1986 as Mayhemic Destruction and released as an album on the band's own label Mega Metal Productions. Reaction to the album was immediate and the band was snapped up for an international album deal by Phonogram Records UK, who then re-released Mayhemic Destruction worldwide in 1987.

Mortal Sin spent much of 1988 recording a second album with producer Randy Burns, who had previously worked with Kreator and Megadeth. The release of Face of Despair was held over until early 1989; shortly afterward the band gained further prominence with an Australian tour with Metallica in May. In January 1990, Mortal Sin toured Europe and the UK then played some shows in the US but after their final show there Maurer quit the band.

On their return to Australia, the band split, only to reform a short time later with Steve Sly replacing Maurer, however by the end of the year Hughes, Burke and Carwana had also been replaced. The line-up of Eftichiou and Sly plus Alex Hardy (guitar), Dave DeFrancesco (guitar, ex-Enticer) and drummer Nash Hall toured briefly and recorded a third album entitled Every Dog Has Its Day (released as Rebellious Youth in some markets) that showcased a more traditional metal style than previously but the new combination and sound ultimately failed and by late 1991 Mortal Sin split up.

The band had a brief resurgence in 1996, when original members Campbell, Eftichiou and Maurer reformed Mortal Sin. They released an EP - Revolution of the Mind independently and launched the first full-scale Australian tour that Mortal Sin had ever undertaken. Eventually the band split up in 1998.

In February 2004, Mortal Sin reunited once more, this time as Campbell, Maurer, Eftichou and former Addictive guitarists Joe Buttigieg and Mick Sultana. A year later, Mortal Sin was inducted into the Hall of Fame at the inaugural Australian Heavy Metal Music Awards but within a month the line-up changed again when Campbell and Buttigieg were replaced by Luke Cook and Nathan Shea. In April 2005, Mortal Sin toured Australia with Anthrax and on February 4, 2006, the band played a show in Sydney that featured them performing the Mayhemic Destruction album live in its entirety for the first time.

In August 2006, the band returned to European stages to play some shows in Germany, firstly with Rock over Hamburg alongside Michael Schenker Group, Rose Tattoo, Metal Church, Victory, Gorilla Monsoon and Tourettes Syndrome. The band also performed at the Wacken Open Air Festival. Mortal Sin's fourth full-length album An Absence of Faith was recorded in February 2007 at The Basement Studios in Sydney with producer Phil McKellar.

In 2011, Psychology of Death was released through NoiseArt Records/Riot Entertainment followed by extensive touring throughout Australia and Europe. Due to various reasons, the band split once more.

In late 2025, Mortal Sin announced their return to the stage in 2026 to celebrate 40 years of Mayhemic Destruction. While the band has had many challenges and triumphs throughout the years their passion and dedication to performing live has never wavered - earning them a title of thrash metal legends in Australia.

Mortal Sin will see the return of original members Mat Maurer (vocals) and Andy Eftichiou (bass), with Nathan Shea (guitar) and Ryan Huthnance (guitar) returning to the line-up. Mortal Sin are excited to welcome Sydney drummer George Delinicolis of LIVEWIRE and Bastardizer to join them on tour.

Mortal Sin’s first show back was at Adelaide’s Froth & Fury Festival in January 2026 - playing classics from their full catalogue. The band has an upcoming Australian tour with additional dates in Europe in April at Germany’s Keep it True Festival and at club shows and festivals throughout August 2026.