The loggerhead turtle, named Tarly, was cared for by staff at Kelly Tarlton's Antarctic Encounter and Underwater World rescue and rehabilitation team and the Department of Conservation.
Prior to the release, the turtle was fitted with a satellite tag which would enable staff at Kelly Tarlton's to track her movements and learn more about these mysterious creatures.
Kelly Tarlton curator Andrew Christie said sea turtles were notoriously secretive and were also extremely threatened with six of the seven species recognised as endangered or critically endangered.
"The more we know, the more we can help protect them ... We expect that, because so little is known about sea turtles, the information we gather from this tag will be of interest to the scientific community abroad," he said.
In the 14 months she had been at the Auckland oceanarium, the turtle had thrived, nearly doubling her weight and hitting the scales at an impressive 80kg, Mr Christie said.
Loggerheads were extremely rare in New Zealand waters.
Tarly washed up on Baylys Beach near Dargaville in November 2007, suffering from dehydration and exhaustion and had large, raw wounds on the back of her head.
A course of antibiotics was administered and she was tube fed a special formula of fluids and prescription cat food to regain her strength.
By late January 2008 she was feeding well and was ready to enter the oceanarium.
Mr Christie said the process of nursing animals like Tarly back to health usually took one to two years, and watching them swim away when released is "both a little sad and extremely fulfilling".
The facility currently had two more recovering turtles - a hawksbill and a green.
The hawksbill turtle is on the World Conservation Union's critically endangered list.
