Poulter survived a late stumble for the second straight day to card a 2-under-par 70 in the final round for an 18-under-par total of 270 at Celtic Manor.
Britain's Jonathan Lomas, Australian Jarrod Moseley and South African Darren Fichardt shared second place on 15 under, Moseley's bogey on the 18th costing him outright second.
The fans hoping to see local favorite Phil Price secure a home victory left disappointed after the Ryder Cup hero faded to a closing 74 to finish six shots back of playing partner Poulter.
Poulter, battling a bout of tonsillitis all week, put himself in place for a win the moment he equaled the course record with a 65 in the first round, a record subsequently beaten by Moseley's 63 on Saturday.
The winner's check lifted the 27-year-old from 135th on the Order of Merit to 14th, and maintains his record of winning a tournament every year since 2000, when he was also the tour's Rookie of the Year.
It also confirmed he had made the right decision in seeking to change his swing under the guidance of coach David Leadbetter, and puts him firmly back among the group of bright English prospects alongside close friend Justin Rose, Paul Casey, Luke Donald and Nick Dougherty.
"I'm back," was Poulter's typically confident statement after ending a run of five missed cuts in six events in style. "When you go through a bad spell people tend to forget about you but if you stick in and work hard you should be back in no time.
"I'm definitely moving in the right direction and it was definitely the right decision to change my swing. I had a few bad weeks and this just proves the work I have done is paying off."
Rose, who will defend the British Masters title, was one of the first to congratulate the winner as he left the 18th green.
"I spoke to him all week and he was keeping an eye on me," said Poulter. "He's doing a company day here on Monday and it was really nice that he got here a few hours earlier than he needed to to watch the last few holes.
"He was really happy for me and I would be likewise the next time he wins. I'm sure we will have some fun when there's a week off shortly."
Poulter also won his first tour title in Morocco while suffering with tonsillitis and admitted he was unsure whether to have them removed at the end of the year.
"I probably shouldn't have played in the pro-am on Wednesday and
to shoot the score I did on Thursday was amazing," he added.
Poulter began the day two shots clear of Price and extended his cushion to three with a birdie on the second after a superb chip from just off the green.
Cheered on by the home crowd, Price hit back with birdies on the third and fifth to close the gap to one, but a bogey on the next gave Poulter breathing room.
Price also bogeyed the eighth and was replaced as Poulter's main challenger by Moseley, who had picked up shots at the third, fifth and sixth holes to lie two shots back.
Moseley then briefly reduced his deficit to one stroke with a birdie on the 11th, only for Poulter to go one better in the group behind with a 60-foot eagle - the only one at that hole all week.
Poulter had been six shots clear after 13 holes of the third round only to drop four shots in the next three holes, and he fell foul of the same stretch again Sunday.
He bogeyed the 15th after finding a greenside bunker and dropped another shot at the next hole - where he took six Saturday - after again going through the back of the green.
That cut his lead back to one, but when Moseley found trouble off the tee on No. 18 and could only bogey, Poulter's birdie was simply the icing on the cake.
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