Feeney, who is managed by Paul Morris, debut in the second-tier this season with Tickford Racing, finishing seventh.
He also made his Bathurst 1000 debut with the Ford squad, combining with James Courtney for an impressive 10th place finish.
The 18-year-old has now been locked in for a Holden switch for Super2 next season, joining Angelo Mouzouris in an expanded T8 line-up.
“It’s hard to put into words how excited I am to join the team in 2021 and to return for my second season in Super2," said Feeney.
"It’s an unbelievable opportunity to be able to join Triple Eight and a dream come true to join such a dominant team.
“I have a clear goal in 2021 and that is to win the Super2 Series. I know Triple Eight will give me the best opportunity to reach that goal.
“I have worked through all of my years of racing to reach the Supercars Championship and now to be aligned with Triple Eight is surreal.
“I can’t thank Roland [Dane] and the entire Triple Eight team enough for giving me this opportunity. It’s been a dream to be a part of this team and it has come true. I must also thank my Dad and Mum who have put everything into me over my whole racing career, as well as Boost Mobile for giving me my first break.
“I finally have to thank Paul Morris who has made everything in my racing career possible. I cannot thank him enough for the opportunities that he has given me and to take me under his wing. Being involved at Norwell Motorplex has led to such great successes – even an introduction to Roland.”
Mouzouris, meanwhile, finished ninth in Super2 this season, having joined T8 straight out of Formula Ford.
He's now looking forward to a second Super2 campaign, this time with a teammate to work with.
“I’m super excited moving into my second tin-top season with Triple Eight, and I can't wait to move forward and build on what I have learnt this year,” he said.
“I just want to see how 2021 plays out. I obviously want to do the best I can on and off the track and continue to improve. There is no set position goal other than to do the best I can, however there are personal goals that the team and I want to achieve.
“I’m excited for Broc to join the team too. It will be great having a teammate to learn off and push myself even further next year."
The 2020 Super2 schedule is yet to be released, however both Bathurst rounds, Townsville, Sydney Motorsport Park and Gold Coast have all been linked to the second-tier calendar.