The 58-test halfback was lured to the Brumbies in 2016 to much fanfare but managed only 18 games in his two seasons.
A serious knee injury sidelined him for most of the current season which wraps up with Saturday's final between the Lions and Canterbury Crusaders in Johannesburg.
"I had a very enjoyable two seasons at the Brumbies and thank everyone connected with the club for their support during my time here," the 28-year-old said in a statement.
Cubelli played in the Brumbies' quarter-final defeat to the Hurricanes two weeks ago but Canberra fans may have another chance to see him when the Pumas play a Rugby Championship match against the Wallabies in the Australian capital in September.
Cubelli's departure will heap more responsibility on young scrumhalf Joe Powell, who acquitted himself well in the Argentine's absence and made his Wallabies debut during the June internationals.
The Brumbies have also released journeyman flanker Chris Alcock, with the former New South Wales Waratah and Western Force player heading to Japan.
World class flanker David Pocock is set to fill the breach next season when he returns to Canberra following a year-long sabbatical.
(Reporting by Ian Ransom; Editing by Greg Stutchbury)
