The Philadelphia ace was an easy choice after leading the league with 21 wins and topping the majors in innings, shutouts and complete games.
Acquired by the Phillies from Toronto last December and immediately given a $60 million, three-year contract extension, Halladay did everything expected of him — and more.
Halladay threw a perfect game at Florida on May 29, firmly stamping this season as the Year of the Pitcher, then tossed a no-hitter against Cincinnati in his playoff debut.
Halladay received all 32 first-place votes in results released by the Baseball Writers' Association of America.
Adam Wainwright of St. Louis was second and Ubaldo Jimenez of Colorado was third. San Francisco ace Tim Lincecum, who won the past two NL Cy Youngs, finished 11th.
Halladay went 21-10 with a 2.44 ERA and 219 strikeouts in his first season in the NL. The 33-year-old right-hander pitched 250 2/3 innings, nine complete games and four shutouts, living up to his billing for excellence and durability.
Voting for the award ended after the regular season. Three days later, Halladay completely overmatched the Reds, the top-hitting team in the NL, in their playoff opener.
Halladay split a pair of matchups with Lincecum in the NL championship series. The Giants won in six games, blunting the Phillies' bid to reach the World Series for the third straight year.
The pitcher nicknamed "Doc" added to the 2003 AL Cy Young he won with the Blue Jays. He joined Roger Clemens, Randy Johnson, Pedro Martinez and Gaylord Perry as pitchers to earn the award in both leagues.
Halladay became the 13th pitcher to unanimously win the NL Cy Young, with Jake Peavy previously doing it in 2007. It has happened eight times in the AL, with Johan Santana last accomplishing the feat in 2006.
This year's AL Cy Young Award winner will be announced Thursday. On Wednesday, the AL and NL managers of the year will be presented.
Halladay is the 16th multiple winner of a Cy Young Award, a list headed by Clemens' seven and Johnson's five. Steve Carlton and Greg Maddux each won four times.
The Cy Young started in 1956. Through the 1966 season, there was just one selection from both leagues.
Halladay was the seventh Phillies pitcher to win the award. Along with Carlton, John Denny won in 1983 and reliever Steve Bedrosian got it in 1987.
Halladay arrived in Philadelphia amid much fanfare. The night of the trade, he received a standing ovation from nearly 20,000 fans when he was introduced in person at a Philadelphia 76ers game.
The Phillies paid a price to get him. They wound up trading 2009 postseason star to Seattle as four teams wound up being part of the swaps.
Halladay was dominant in an opening-day victory at Washington and won his first four decisions. The next month, he threw the 20th perfect game in major league history — only after got pinch-hitter Ronny Paulino to hit a grounder for the final out did Halladay break into a big smile.
It was a rare show of emotion. Halladay is well known for his focus and dedication to workouts. In spring training, it was not uncommon to see him in camp by 6 a.m.
Halladay earned his 18th win in mid-September. Despite all of their recent success, no Phillies had reached had won more than 17 since 1983, when Denny did it.
The only pitchers picked on all the ballots were Halladay, Wainwright and Jimenez. There were two BBWAA voters in every league city, and each person listed five top choices.
Halladay finished with a perfect 224 points. Wainwright (20-11, 2.42 ERA) got 28 second-place votes and 122 points and Jimenez (19-8, 2.88 ERA) got the other four seconds and 90 points.
At one point, Jimenez appeared to be a sure thing for the award. He started the All-Star game with a 15-1 record but tailed off.
Atlanta's Tim Hudson (17-9, 2.83) was fourth and Florida's Josh Johnson, who led the NL with a 2.30 ERA, was fifth. Giants closer Brian Wilson, who led the majors with 48 saves, was highest-finishing reliever at seventh.
Halladay received a $250,000 bonus, and Wainwright and Jimenez got $100,000 each.
By finishing second, Wainwright's $9 million option for 2012 and $12 million option for 2013 become guaranteed as long as he doesn't finish the 2011 season on the disabled list because of an injury to his right arm.