Smyth was born in Northern California and started his career in the female-fronted melodic progressive metalband Ariah after graduation in 1988. Ariah never released an official studio album, but they recorded a few songs and played local shows with bands like Vicious Rumors and King Diamond. Ariah disbanded in 1992.
After a three-year hiatus, he joined the power metal band Vicious Rumors to replace guitarist Mark McGee who had left the band after the death of Vicious Rumors vocalist Carl Albert. Something Burning (1996) was the first album which Smyth played on. It was followed by Cyberchrist in 1998, and now he participated in songwriting too.
In 1999 Smyth left Vicious Rumors and joined Testament. The Bay Area thrash legend had just released The Gathering album, but lead guitarist James Murphy was diagnosed with a brain tumor, so Testament were in want of a new guitarist for the forthcoming tour. In the next 5 years Smyth toured with Testament all around the globe and played uncountable shows as a member of the band. He wanted to make a studio album with Testament but that remained a dream for him.
On the other hand, Smyth formed the band Dragonlord as a side project with guitarist Eric Peterson and bassistSteve DiGiorgio of Testament in 2000. This symphonic black metal outfit have released two albums: Rapture(2001) and Black Wings of Destiny (2005).
Seattle-based Nevermore had been friends with Smyth prior to his joining of the band. Initially jokingly, he asked if he could join Nevermore. He joined Nevermore as a touring guitarist, and in 2004, Smyth officially joined the band after helping them tour in Europe. He played guitar in the band along with Jeff Loomis and co-wrote some songs on the critically acclaimed album This Godless Endeavor (2005).
In the summer of 2007 Smyth left Nevermore due to “personal and business differences”. At that time he was working on an all-instrumental album in the vein of progressive rock with his former Ariah bandmate and bassistSteve Hoffman. This side project was named “EssenEss” after their same first names, as a transctiption of S’n’S (Steve and Steve). Self-titled The EssenEss Project debut album released on November 5, 2007.
Steve started an international metal band with classic and modern influences, featuring members carefully selected by Smyth: Mikkel Sandager (MERCENARY) on vocals, Jamie Hunt (BIOMECHANICAL) sharing guitar duties, rounded out by a powerhouse rhythm section with Tomas “O’Beast” Koefoed (MNEMIC) on bass guitar and Michele Sanna on drums (although former drummer Raphael Saini of Italian progressive metallers CHAOSWAVE played on the album). 
Their debut album “The Distortion Of Lies And The Overdriven Truth” was released on February 18, 2014 via Scarlet Records. The CD was recorded and produced by Steve Smyth and was mixed by Roy Z (JUDAS PRIEST, BRUCE DICKINSON, HALFORD). It was mastered by Alan Douches at West West Side Music, with artwork created by Niklas Sundin from Cabin Fever Media , complemented with photography from Anthony Dubois. 
In 2014 he joined the thrash/death metal supergroup “From Hell” alongside Damien Sisson of Death Angel and Paul Bostoph of Slayer and Testament fame. Debut album “Ascent From Hell” was released on April 8 via Scourge Records.