Dr Piukala was elected by Health ministers and other senior officials from the Region's Member States on 17 October.
He is the first Tongan and Pacific person to take up the regional role.
It is expected that he will take office as the Regional Director on 1 February next year, for an initial term of five years.
Dr Piukala said he wished to continue his work in Tonga as the Minister of Health, before embarking on his new journey.
The WHO Western Pacific Region is home to more than 1.9 billion people across Asia and the Pacific.