The Tahs dominated the Brumbies scoring three tries to one in their 26-8 victory to earn their place against the seven-time champions at Sydney’s Allianz Stadium.
Alofa Alofa, Kurtley Beale and Bernard Foley crossed for the hosts while the lead was stretched by three penalties and a conversion from Foley’s boot.
Henry Speight scored the only try of the match for the Brumbies while Christian Leali’ifano managed the solitary penalty.
In the other semi-final New Zealand’s Crusaders smashed South Africa’s Sharks 38-6 for their place in the final.
It will be the first time the seven-time champions have appeared in the championship decider since 2008.
After topping the table at the end of the regular season the Waratahs earn the right to host the Canterbury side led again by All Blacks skipper Richie McCaw.