Gregg is a native of New Orleans. He grew up near Pittsburgh, Pennsylvania and southeastern Minnesota. He graduated cum laude from Mankato State University in Mankato, Minnesota, and based on his academic standing was a member of the Law Review at Hamline University School of Law, from which he graduated in 1979. After law school, he worked for 7 years in the United States Department of Justice in Washington, D.C., representing the United States in trial and appellate courts across the country. In 1987 he began in private practice in Charleston, SC, where he raised five children and served on the Charleston County School Board from 1996 to 2010. He is admitted to the state bar of Minnesota and South Carolina, the federal courts in each state, the Fourth Circuit Court of Appeals, and the United States Supreme Court. His areas of practice include sexual abuse, police misconduct, defamation, False Claims Act (whistleblower) cases, general negligence, personal injury, and construction claims. He is an AV rated lawyer, the highest available peer review rating from Martindale Hubbell, which requires a lawyer be admitted for 10 years or more and for his peers to rank him at the highest level of professional excellence and ethics.