The 24-year-old from Worksop, whose pounds 83,000 winner's cheque means that he won more than pounds 500,000 in November, pegged the world No 1 back on the final hole to force the play-off after a head-to-head struggle over the last round.
It was Westwood's cool nerve that prevailed as Norman faltered on the fourth extra hole, taking three putts and allowing Westwood to seal victory with three-foot putt.
Westwood has finished an arduous 36-tournament season with a rousing flourish following his wins in the Volvo Masters in Spain and another play-off at the fourth extra hole to win the Taiheiyo Masters in Japan.
"It's been incredible, really," Westwood said. "My coach [Peter Cowen] said before the Volvo Masters, `Come on, you can win two of these last five' because I always play well at the end of the year. I've ended up winning three and finishing second in the other one."
Westwood's win deprived Norman of a sixth Australian title and third in succession. Asked about the pressure of playing Norman in a play-off before a large gallery of his supporters, Westwood said: "The pressure's off then really, the worse you can finish is second. I've played three, won three - I don't mind play-offs, I enjoy them."
Both players finished the 72 holes tied on 14-under 274 - Norman compiled a closing one-over 73 and Westwood a par 72. But Norman opened the door after leading thoughout the final round, with three putts at the 18th to drop a shot; Westwood had a par.
The Australian, Craig Parry, finished third, a shot away with 65 to finish 13 under on 275, while Scotland's Andrew Coltart was sixth after a 71 left him on 280.Reuse content