The 6-8 star forward from Bremerton (Wash.) High highlighted the reasons for his decision.
"Growing up as a kid, North Carolina was my favorite school," he said. "The coaches have a great program, really nice players and I do have family there."
Williams spoke of how much Roy Williams influenced his decision.
"He was definitely a big factor - he's a great guy and I really like him," Williams said. "He brought his wife with him [when he came to my games] - that was very impressive to me."
His official visit to Chapel Hill also went a long ways in helping him decide to be a Tar Heel. Williams said the highlight of his visit was playing with the players and spoke of how much he likes his new teammates.
But there was one thing the UNC head coach did during the visit that spoke volumes for Williams.
"He let me study for a couple hours and that meant a lot to me," Williams said.
Williams said he made the decision about a week ago and called Roy Williams within the last few days to tell him the news.
"Once I told him he dropped the phone and started screaming," he said of his new head coach's reaction.
But the decision to leave his home state was far from easy for the family-oriented all-american.
"The hardest thing will be leaving my mom and brothers," Williams said. "I thought about it but I had to do what was best for me."
And does he expect to see a lot of playing time as a freshman?
"To be honest, playing time is a factor but I know they're not going to just give it to me," he said.
Special thanks to Nathan Joyce for his help.
Check out IC's Marvin Williams profile.