Having seen his side fight back from losing the opening Test in Brisbane with a battling 16-15 triumph in Melbourne, Deans' job was completely undermined by a record 41-16 defeat in Sydney in last weekend's series decider at the ANZ Stadium.
His decision to step down in the wake of the defeat, which saw the Lions wrestle the Tom Richards Trophy out of the Wallabies' hands after a 12 year reign, was announced on Tuesday and brought to an end the longest sequence of any national coach in Australia. Deans took charge of the3 Wallabies in 74 Test matches after taking over the job in the 2008 season.
The former All Blacks full back, who is still the most successful Super Rugby coach in the tournament's history, broke new ground when he became the first non-Australian to land the country's most coveted coaching position five years ago.
He won a Tri-Nations title in 2011 and led the wallabies to third place in the Rugby World Cup later that year. No sooner had Australian Rugby Union chief executive Bill Pulver thanked Deans for his efforts in one press release, than a few hours later he welcomed former World Cup winning Wallaby prop McKenzie into the role in his place.
McKenzie becomes the first former Australian international installed in the job since Dave Brockhoff coached the Wallabies to a Bledisloe Cup success in his final year at the helm in 1979. His appointment was endorsed by the ARU board after receiving a recommendation from ARU Pulver.
With Deans' contract due to expire at the end of 2013, an advisory group approved by the Board had been assessing the coaching position and potential candidates - including Deans - as the season progressed.
"We have been conducting that due diligence over the last few months, taking into account broad criteria for coach selection. Consideration was given to leadership skills, discipline, coaching capability, coaching records, and important factors such as character, values and style of play," said Pulver.
"Therefore, we were well prepared depending on how the year unfolded. Robbie resigning in the wake of the Lions Tour did not catch us unprepared to move forward with a replacement.
"Having established the necessary criteria, and spoken to the relevant people, we were convinced that Ewen was now the man to take the Qantas Wallabies forward. His opportunity comes forward quickly, with the Rugby Championship and the opening match of that competition - the Bledisloe Cup showdown with the All Blacks on 17 August.
"In welcoming Ewen, ARU also wants to say a sincere thank you to Robbie Deans for his massive contribution to the game in this country over a long period of time. Robbie came into the job in 2008, improved our away record almost immediately, delivered a Tri Nations title in 2011, and has been a significant part of a Lions Tour that over shadows any other Rugby event in Australia since the 2003 Rugby World Cup."