Gregg was born in Selma, Alabama, but spent the majority of his childhood in Henderson, Kentucky, a place he holds dear as his hometown. During his formative years, he attended Henderson County High School, where he developed a passion for creative expression by writing plays, acting in school productions, co-founding a theater company that produced plays for children, and even participating in a state-wide speech and drama competition, ultimately finishing in second place. Additionally, he was an avid player of Dungeons and Dragons.
As he grew older, Gregg's dreams of attending the University of Southern California School of Cinematic Arts remained strong, but financial realities ultimately led him to Western Kentucky University instead. In his freshman year, he was an integral part of numerous theatre productions and was awarded the theatre and dance department's most prestigious honor. Feeling a sense of accomplishment, he decided to switch course after just one year of college and, in 1985, joined the Army, where he attended the Department of Defense Defense Language Institute to study Persian-Farsi and graduated from Army Survival School. He was stationed with a Special Forces group as an Intelligence specialist and was honorably discharged after four years, with enough resources to pursue his dream of attending film school.
Gregg then relocated to Orlando, Florida, and enrolled in film school at Valencia Community College and the University of Central Florida. For the next decade, he worked as a set dresser and prop man on features and TV shows in Orlando and Los Angeles before producing The Blair Witch Project, a film that revolutionized the "found footage" or "cinema scarité" genre. As of 2013, he resides in Portland, Oregon.
