He is rumoured to be one of the candidates for a seat with Richard Petty Motorsports next year, where a void will be left by Kasey Kahne's departure to a Chevrolet team.
However, Ambrose says his future is not yet decided and that a return to Australia is still an option.
"It has been a great five-year journey for me and JTG Daugherty Racing," Ambrose said. "I am proud of being their driver and of what we have been able to accomplish together. I want to personally thank Tad, Jodi, Brad and the entire race team for everything they have done.
"Our plan is to complete the season with the same desire and commitment, and end our relationship the same way it started - with a positive attitude and the willingness to win. I will do everything I can to help JTG Daugherty transition into next year with their new driver.
"After five years, I personally felt it was time for a change. I have no firm plans of what will come next for me and my career. I would like to continue in NASCAR and finish off what I started, but I have not discounted returning to Australia. I'm grateful to JTG Daugherty Racing for giving me an opportunity to become a NASCAR driver and I wish them the best in the future."
Following a strong first full Cup season in 2009, where he ranked 18th in the final standings, his team targeted making the Chase this year - a goal that is now out of reach as he sits 27th in the points, with two top 10 finishes at Richmond and Sonoma his best results.
"Marcos is a friend and he is a great talent," said JTG Daugherty Racing co-owner Tad Geschickter. "He will be an asset to his next team. While we hate to see him move on at the end of the season, we will remain focused on winning races with Marcos."
Ambrose narrowly missed out on his and JTG Daugherty's first Cup victory last month when his car stalled while saving fuel in the closing laps at Sears Point, where he had been dominant throughout the weekend.
He will start as one of the favourites to win at Watkins Glen in a fortnight - the scene of his two Nationwide wins and where he has finished third and second in the Cup events of the last two years.
He was also part of a Goodyear test at the venue, where he swapped cars with Hendrick Motorsports Jeff Gordon, impressing the four-time champion.
Ambrose eager for strong showingDiarra plans Mourinho talks
