The reigning Super2 champion has enjoyed an impressive rookie main series campaign with WAU, a podium and four Top 10s helping him to 18th in the points heading to Bathurst.
That promising form has earned him a second season alongside Chaz Mostert.
“I’m super excited to be back with Walkinshaw Andretti United. I love it here, it really is a family, and it’s fantastic to be able to continue the journey we started," said Fullwood.
“I’ve been really happy with how this year has gone so far, and I’m excited to continue to build during the off- season.
“Having that certainty about my future will allow me to prepare in the best possible way for 2021, so it’s great to get the news out there, focus on this weekend, and then get to work on next year immediately.
“I can’t thank the team and our partners enough for their continued support, and look forward to seeing what the future has in store for us.”
According to WAU co-director Ryan Walkinshaw, retaining Fullwood for a second season is a "no-brainer".
“Re-signing Bryce was an absolute no-brainer," he said. "He has done an outstanding job this year, exceeding expectations and continually performing to a level well above his experience.
"To get a podium in your rookie season is no mean feat, but that is just one of the many aspects we have been impressed with throughout the year.
“He has been a fantastic asset to our team, both on and off the track, and I can’t wait to see his progression continue within our family."
Follow directors Michael Andretti and Zak Brown both backed the decision to continue with Fullwood.
“It’s fantastic to have Bryce re-sign with Walkinshaw Andretti United," said Andretti.
"He has definitely surprised a few people so far in 2020, but we knew from a very early stage that he is a great talent and person, which made the decision an easy one. I can’t wait to see his career continue to grow within our team."
“I’m so excited to see Bryce continue on with Walkinshaw Andretti United," added Brown.
"Not only has he been a fantastic addition to our team this year, punching above his weight in terms of results, but he is a quality person, and an ultimate professional.
“It’ll be fantastic to see that continue next year, but I’m equally excited to watch how both cars go [at Bathurst] this weekend.”