The 51-year-old, a regular on the US Champions Tour, made a 10ft birdie putt on the 18th hole in regulation for a one-under 71 to match Ogilvy at 12-under 276 in the rain-delayed tournament. Ogilvy finished with a 66.
Both players parred the 18th hole on the first hole of the play-off but Ogilvy three-putted for a bogey on the second extra hole to give Senior his third Australian PGA title. He won 21 years ago at Riverside Oaks and the 2003 tournament at Coolum.
"What a great way to finish the year," Senior said. "Geoff hit a pretty indifferent iron shot into 18 but I would have rather made my (birdie] putt instead of Geoff three-putting, but that's what happens."