The 32-year-old North Lanarkshire Leisure-attached player beat overnight leader Alastair Forsyth at the second extra hole after the pair had tied on 15-under-par at the Dundee venue.
O’Hara signed off with a bogey-free 69 to finish with his 277 total, which Forsyth, the 2000 winner, was on course to beat until a double-bogey 7 at the 14th left him having to settle for a closing 71.
After halving the first hole in a sudden-death shootout, O’Hara claimed victory with a par at the second to claim his first title triumph in the Tartan Tour’s flagship event.
“It is brilliant to win this event as it was almost getting like the Scottish Amateur, having lost three times in the final of that back in the day,” he said of defeats in 2004, 2006 and 2009.
“It was starting to feel a bit similar in this event after I lost in a play-off to Gareth Wright in in 2016 then finished second last year. I tried really hard today to keep grinding away and to be make four birdies and also be bogey-free was very satisfying.”
Forsyth, who started the day with a one-shot lead, fell agonisingly short in his bid to round off a brilliant season by adding to wins in both the Northern Open and the PGA Professional Championship.
“Big Al has been playing great this season and any time you finish ahead of him, you are going to be there or thereabouts,” added O’Hara.