In the best barrel conditions of the tournament, Slater won a high-scoring final over Parkinson at Kirra Point to take out his fourth Quiksilver Pro title.
Eleven-times world champion Slater scored 18.56 out of 20 for his two best waves, including a near-perfect 9.83, against Parkinson's 17.47.
The world championship now moves to Victoria for the Rip Curl Pro at Bells Beach from March 27 to April 7.