Aron will remain on the team's board of directors and said he has increased his ownership stake in the franchise. Aron was part of the ownership group that bought the franchise in 2011.
Led by majority owner Josh Harris and Aron, the new ownership group attempted to win back fans with slashed ticket prices, confetti cannons, and other fan-friendly promotions such as reconnecting with past stars.
Aron tells The Associated Press it was his decision to step aside as he pursues another business interest.
"It's a move of my making," he said. "I wasn't pushed, shoved or asked to go."
O'Neil, a Villanova graduate, helped stabilize the New York Knicks after Isiah Thomas left the franchise. He worked as senior vice president for team marketing and business operations for the NBA from 2004 to 2008.
O'Neil was named MSG president in July 2008 and resigned last September. He oversaw the business operations of the Knicks, New York Rangers, and New York Liberty.
O'Neil also has local ties from his job as vice president of sales with the Philadelphia Eagles. He started his career as a marketing assistant for the New Jersey Nets.
The Sixers are the only NBA team without a coach, more than two months after Doug Collins resigned. The Sixers hired Sam Hinkie away from Houston and named him president and general manager in May. Hinkie traded All-Star guard Jrue Holiday to New Orleans on draft night for the rights to Kentucky center Noel Nerlens, a clear signal a rebuilding effort was officially underway after a 34-48 record last season.
"I think there's a plan from Sam where this team will emerge over the next couple of years to be really competitive," O'Neil said by phone. "Hopefully, it will create a really a sustainable, elite basketball team. I think we've got some good opportunities on the business side to grow alongside the team."
Hinkie will continue to make the day-to-day basketball decisions.
O'Neil said he was inspired by former Sixers president Pat Croce, who often used motivational stunts like climbing the top of the Walt Whitman Bridge to generate publicity for the team.
"I was marveled with how he captivated the city," he said. "He liked scaling down bridges. Now, that's not me. But do I engage fans? Of course. I'll certainly be a visible face of the franchise for sure. This is about making sure we get every advantage as a basketball group."
Aron, the former chairman and CEO of Vail Resort, served the last two years as the face of management. He was a constant presence at games, always on Twitter and dreaming up everything from mascot contests to bringing out Big Bella, "the world's largest T-shirt launcher."
It was all good fun when the Sixers reached the Eastern Conference semifinals in 2012. But when the losses piled up last season after the deal for Andrew Bynum backfired, Aron's rah-rah attitude became an easy target for fed-up fans.
Aron will become chairman and CEO of a new investment fund backed my some members of the Sixers ownership group.
"I could have remained in position as CEO of the 76ers, but this is what I wanted to do," he said. "It was always in my mind to see what I could be doing next with the owners of the Sixers from Day 1. If anything, I accelerated the timetable to move on when the opportunity became real to move on in this new investment role."