Howell beat a low-scoring field with eight birdies in his final round and made par at the 18th to clinch the title. He ended the tournament at 23-under-par 265 for his second career victory.
The Englishman finished one stroke ahead of 2001 champion John Daly (64) and Australian Brett Rumford (65) at Golfclub Munchen Nord-Eichenried.
Niclas Fasth (64) and Soren Kjeldsen (66) shared fourth place at minus-21, and Paul McGinley (65) ended alone in sixth place one stroke further back. Simon Dyson shot the day's low round at 10-under 62 to finish in seventh at minus-19.
Overnight leader Luke Donald struggled to a 1-over 73 and ended in a tie for 11th place at 16 under.
Dyson was in the clubhouse with the lead after his exceptional round, which included back-to-back eagles at the fifth and sixth holes. But with the course yielding a lot of red numbers, it looked like the winner would probably have to shoot at least 22 under.
There were more than a few players scattered about the course who were within striking distance of the lead, but the tournament really became a two-horse race between Howell and Daly.
And it was Daly who was continually playing catch up.
After Howell reached minus-21 with his sixth birdie of the day at the 11th, Daly joined him there with a birdie at the 14th. Howell then collected consecutive birdies at 13 and 14, reaching 23 under when he ran home a 20-foot uphill birdie putt at the latter.
It was a good thing, too, because two holes ahead Daly dropped in a short birdie putt at No. 16 to get within one shot at minus-22.
'I knew the guys would be making plenty of birdies, so they weren't going to make it easy for me,' acknowledged Howell.
But Daly never could pull even with the leader. He came up short of the green with a fairway wood at the 567-yard par-5 18th and chipped within 6 feet for a chance at birdie. But the putt went left, and he finished with par.
Rumford chipped inside Daly at the last to finish with a birdie and tie his playing partner at 22 under.
So all Howell needed to do was par out for the win, and that's exactly what happened. Although not without a little drama.
At the par-4 16th, Howell's second shot landed close to the hole but spun away and was only saved from the greenside water by a patch of fringe. He then chipped within 2 feet before curling in his putt to save par.
'I hit it perfect and it just kept coming back,' Howell said of his wedge shot. 'The crowd cheered, and then booed, and it just hung there.'
Howell went on to par the 17th for the fourth straight day after landing his tee shot in the middle of the green.
'I don't hit as many greens as the top players, but this weekend my ball striking was far, far better,' admitted Howell. 'I hit a lot more greens.'
At the 18th, Howell drove the fairway and played it safe by laying up short of the green with his second shot. He then chipped within 15 feet before leaving himself with an uphill knee-knocker of about 18 inches to make par.
The putt split the cup for the win.
'I was shaking like a leaf. I'm just so glad it went in,' said Howell, whose previous win came at the 1999 Dubai Desert Classic. 'Let me tell you, it's been a long journey. I've played some great golf, but getting that [second] win has obviously been a sticking point for me.'
Donald played along side Howell and opened with four straight pars before a birdie at No. 5 put him at minus-18. But the overnight leader stumbled to a double bogey at the par-5 sixth when his second shot rolled into the water, and he would not be a factor the rest of the day.
Simon Khan shot a final-round 69 to finish alone in eighth place at minus-8. Bradley Dredge (68) and Raphael Jacquelin (67) tied for ninth place one stroke further back, and four golfers shared 11th place with Donald at minus-16.