The news was confirmed in a Facebook statement by the band, which read, "It is with great sorrow to announce the passing of our friend and band member, Phil McCormack.
"Our condolences and prayers go out to his family during this time of loss. Phil's contributions to Molly Hatchet were heard around the world. He will be missed but never forgotten."
McCormack briefly joined Molly Hatchet in 1992 as a temporary replacement for original singer Danny Joe Brown, and became a full-time member in April 1995 after Brown departed permanently for health reasons.
Since joining the band he has performed on seven albums: Devil's Canyon, Silent Reign of Heroes, Kingdom of XII, Warriors of the Rainbow Bridge, Southern Rock Masters, Justice and Regrinding the Axes.
Prior to joining Molly Hatchet, he was a member of fellow Southern rockers The Roadducks, appearing on their 1987 album Get Ducked, and played with Savoy Brown, singing on two tracks on their 1992 album Let It Ride.
The Roadducks released their own statement, saying, "Phil was a fabulous, singer, band mate, brother, and human being. Collectively we spent thousands of hours that turned into thousands of days together, creating an unbreakable bond few people are fortunate enough to ever experience.
"I will close with lyrics from one of our all time favorite songs. A song I will always hear Phil singing "Won't you bury me with my chaps on, and my six-gun by my side ...hidin in the Desert Skies."
Last November Jimmy Farrar, who sang with Molly Hatchet between 1980 and 1982, died at the age of 68.
This followed the deaths of founding members Dave Hlubek and bassist Banner Thomas in 2017, and drummer Bruce Crump in 2015. Danny Joe Brown died in 2005, while guitarist Duane Roland passed away in 2006.