Mr Brown told Radio New Zealand it was the only suitable option for his needs.
"I would like to get myself into an electric car, but it's the mayoral car so I tend to have a number of councillors or community members with me at any one time," he said.
The mayor's office said that despite a thorough investigation, no other vehicle was found to better fit the purpose of carrying up to five adults with space to also work.
"I hope people are accepting of the fact that a black Holden is probably mid-range and good in the circumstances for the mayor of Auckland to get himself around from one place to another," Mr Brown said.
In May 2005, former Auckland City mayor Dick Hubbard replaced the mayoral gas-guzzler with a hybrid electric Toyota Prius.
At the time he said: "We are going to have to be mindful of air quality problems and it's hugely important that we put emphasis on vehicles that are highly efficient when it comes to emissions and emission control."