"This hasn't been an easy decision for either party but it became apparent over our discussions that it would be best for Andre and his career to start a new chapter and challenge," team co-owner Stephen Grove said.
"When the time comes, he will leave us with my blessing and huge goodwill from every single member of the team.
"We're proud of everything Andre has achieved with Kelly Grove Racing, but for now, we continue to focus on the rest of the 2021 championship and finishing as strong as possible."
Heimgartner scored his first Kelly podium in 2019
For some time, it appeared Heimgartner was set to race on into 2022 with the team.
However, the team - which will be a solely Grove-run operation from 2022 - confirmed Heimgartner will leave Braeside at season's end.