“We've toppled the high wall of ideology,” said Ko as he addressed his jubilant supporters in a concert-like rally after preliminary results showed that he won by more than 240,000 votes.
“I promise that I'll be a mayor of all citizens,” he said, reiterating his election platform of transcending all party boundaries.
DPP Chairwoman Tsai Ing-wen led ranking party officials to thank supporters as they celebrated the victory.
The ruling KMT managed to maintain control in one of the six special municipalities, New Taipei, only after a much tougher-than-expected battle.
The results mean the number of KMT-controlled local governments has been reduced from 15 to six.