The 38 year old carded a four under par final round 68 to overcome his countryman and first round leader Bradley Dredge, finish on a winning total of 14 under and earn a place in Paul McGinley's European team.
With so much at stake, Donaldson showed the poise and determination of a future Ryder Cup star and raced out of the blocks, starting with three successive birdies before a bogey at the fourth pegged him back to two under for the day, having found the trees from the tee.
He claimed that shot back, however, with a three at the par four sixth hole to reach the turn in three under, before rolling in a putt from 25 feet at the tenth for birdie and capitalising on the final par five, the 13th, for another gain.
A bogey at the tricky 17th hole did not prove costly for Donaldson as Dredge also ran up a five after driving into the water hazard and a par at the sealed the title and a place at Gleneagles.
"This is big. It's been an amazing week, I didn't get here until late, I needed to play well either this week or next week, or both, to guarantee my place in the Ryder Cup team. So there was a lot on the line and I had to play well and this week I played really well, so that's great.
"Winning is everything, wins shoot you up world rankings, The Race To Dubai, all sorts. It's massive, very important, those three last holes coming in there were really tough with the wind blowing, so I'm just really happy to seal it.
"It's so difficult to get into the team, the lads are playing so well. I played a couple of weeks there in Germany and France, and then I should've maybe taken a week off and didn't, I went to Scotland thinking I was playing well, and then when I got there I wasn't at the races. The form then followed on and I was a bit tied, didn't play well at The Open.
"Suddenly you've missed two cuts at two big events and slipped down the Rankings a bit, and it's all to play for. You know that you have to play well to secure your place and it did come down to the wire.
"But that's how it is to get into the team. I played as well as I can play for 18 months, and then a couple of slow events and you rocket down the list, so it's great to come here and play so well and do enough to get into the team."
The two Australians in the field, Nathan Holman and Wade Ormsby both missed the cut.
The European Tour now moves to Torino in Italy for the Italian Open.