He beat other candidates, Tim Hanna and Don Byars, for the job.
After hearing the news of his success, he said he was very happy.
Gary Tong had a cozy celebration with his family after being re-elected.
"I'm very happy and proud to be able to represent Southland again. I appreciate those who voted and I'm looking forward to leading council through this triennal."
He confirmed this would be his last term as mayor.
"A further re-election is definitely not gonna happen. I'm not gonna standing again for Southland District Council - I think that is time to hand over because nine years is sufficient."
Mr Tong had previously told ODT he would not be seeking a fourth term as mayor, which would mean this third term would be his final - the 60-year-old was first elected in 2013.
He had said he didn't want to leave while he had projects unfinished.
"I am re-standing to continue with the road I'm on at the moment, to finish the projects that have been started during my last six years."
"I don't want to leave now and leave these projects in the air."
"I've got a lot of irons in the fire - some of them are out in the public arena, some are not."
