He made the comments during a guest blog post on the Friendly Atheist's Patheos site, claiming:
"The Christian music scene is populated by many people who act as though they have a direct hotline to a God who supplies them with the answers to the Universe.
"There seems to be more ego and narcissism amongst Christian musicians than their secular counterparts."
The co-founder of the Christian band left the group in 1990 and returned to Australia.
He studied human psychology, got married and had two children, but his marriage ended in 2003.
He says by 2007, he had "renounced Christianity once and for all" and declared himself an atheist:
"I always felt uncomfortable with the strict rules imposed by Christianity.
"All I wanted to do was create and play rock and roll... and yet most of the attention I received was focused on how well I maintained the impossible standards of religion. I wanted my life to be measured by my music, not by my ability to resist temptation."
He added that certain influences had a great effect on his attitude to religion, saying he became "fascinated by the works of Carl Sagan, Neil deGrasse Tyson, Lawrence Krauss, Brian Cox, and Richard Dawkins."
He also attacked former co-members of the Newsboys:
"The truth is - from someone who knows what went on then and what goes on now - the Newsboys aren't as holy as they profess. Instead of wearing a mask of 'righteousness', they should acknowledge that they are struggling as much as everyone else."
The band has had six number one Christian singles, although many musicians have left and joined over the years.
Newsboys is currently made up from musicians Michael Tait, Duncan Phillips, Jeff Frankenstein, and Jody Davis.
None of the original band members remain.
Current co-manager of the Newsboys, David Wagner, says he doesn't wish to comment on the blog post, describing George Perdikis as "a former member who we haven't had any interaction or heard from in more than 20 years."