Deans stood down following the Wallabies' 2-1 series defeat against the British and Irish Lions and the Australian Rugby Union has now confirmed former Test prop McKenzie as his successor.
ARU chief executive Bill Pulver said: "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."
Deans' resignation came after the Wallabies' 41-16 defeat in Saturday's third Test against the British and Irish Lions in Sydney, which saw the tourists complete a 2-1 series win.
An ARU statement read: "Qantas Wallabies head coach Robbie Deans has announced this morning [Tuesday] he is stepping down from the role effective immediately."
The governing body had already been reviewing Deans' performance as he approached the end of his contract, which was due to expire at the end of the year.
"We have been conducting that due diligence over the last few months, taking into account broad criteria for coach selection," Pulver said.
"Consideration was given to leadership skills, discipline, coaching capability, coaching records, and important factors such as character, values and style of play.
"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.
"(McKenzie's) opportunity comes quickly, with the Castrol EDGE Rugby Championship and the opening match of that competition - the Bledisloe Cup showdown with the All Blacks on August 17."