Killswitch Engage formed in 1999, in Westfield, Massachusetts, after the disbanding of the two bands Overcast and Aftershock.

In 1998 when Overcast split, D'Antonio started his search to find the right people to fuse hardcore and metal with melody.
D'Antonio got in contact with Adam Dutkiewicz, and Joel Stroetzel, the drummer respectively guitarist for Aftershock. The band was completed when Jesse Leach, vocalist for Corrin and Nothing Stays Gold joined.

The band’s name comes from an episode of the television series The X-Files entitled “Kill Switch”.

After the release of their debut album Alive Or Just Breathing and the following tour, in 2002 – Jesse Leach quit Killswitch Engage due to struggles with straining his voice combined with being a newly-wed, with his wife missing him.
Leach was soon replaced by Howard Jones.

After nine years of service and taking the band to fame, Howard quit the band in 2012. He later stated it was due to the heretic lifestyle in combination with his diabetes.

To replace Howard, the band held auditions for a new vocalist. They had a lot of applicants at try-outs, but they wound choosing their former vocalist – Jesse Leach.