The Spaniard defeated Finland's Mikko Ilonen on the third hole of a sudden-death play-off to make up for missing out 12 months ago when England's Chris Wood fired an eagle on the 72nd hole to beat Garcia and George Coetzee by a shot in Doha.
A flawless closing seven-under-par 65 saw Garcia set the clubhouse target of 16 under, but the 33-year-old crucially missed from eight feet for a birdie on the last and then looked on as Ilonen birdied the 16th and 18th to com- plete a 66 and force extra holes.
The players returned to the 18th for the play-off and both found the green on the par five in two, Ilonen missing his eagle attempt from 25ft before Garcia did likewise from half the distance.
A second visit to the 18th failed to identify a winner, Ilonen missing an eagle attempt from 25ft after Garcia had got up and down from a greenside bunker. However, the third extra hole proved decisive as Ilonen found the same bunker and was unable to rescue a birdie, leaving Garcia a tap-in to secure an 11th European Tour title - and his first since October 2011 - after his long eagle putt had narrowly missed.
Thorbjorn Olesen had a great chance to join the play-off but missed from 12ft for an eagle on the 18th. The Dane shared third place with joint overnight leader Rafael Cabrera-Bello.
Cabrera-Bello also needed an eagle on the 72nd hole to catch Garcia and Ilonen, but saw his chip from over the green pull up three feet short of the hole.
"It feels good," said Garcia, who will move from 11th to inside the world's top 10 when the rankings are updated tomorrow. "It's funny as I started the day thinking if I could shoot six or seven under maybe I would have a chance.
"I had a very similar putt to what I had last year to get it to 17 under on 18; I hit a good putt and unfortunately it didn't break. The up and down from the bunker in the play-off was key and I'm very happy to be able to win it."
Asked about the pressure of contesting his seventh European Tour play-off - having previously won two and lost four - Garcia said: "I almost feel less pressure because you feel like you've had a great week already and if you win it's kind of like a little bit of a bonus. I was definitely more nervous on my tee shot on the 18th [in regulation] than in the play-off. That's probably why I hit three better tee shots."
Garcia had not finished outside the top 25 on his previous seven visits to Qatar and added: "I have always said it's a golf course I enjoy and I am very pleased to finally be able to get my hands on the trophy. We've been coming here for eight years and have been quite close to winning before."
Ilonen had looked like missing out on his first European Tour play-off when he hit a poor bunker shot on the last hole of regulation, and although he holed from 20ft for birdie on that occasion, a similar effort from the same hazard on the third play-off hole proved decisive.
"I was expecting one of us would need to make an eagle to win it," said the former British Amateur champion. "I hit two poor bunker shots out of the same front right-hand trap, one in regulation and one in the play-off, and I'm not going to blame anything else. I came up two short of my target in regulation, I thought 64 would do it outright, but Sergio was a bit better than me this time. I played good golf this week, so I can't be too disappointed.
Paul Lawrie finished joint 11th after a 70 left him four shots behind the leaders.