Johnson, the 6-foot-7 ace of the Marlins' staff, posted a 3-0 record and a Majors-low 0.88 ERA in his first six starts, all quality efforts. His 18 hits allowed were the fewest since 1900 by a pitcher with a minimum of 40 innings pitched before May 1.
Milwaukee's Ryan Braun, meanwhile, took home Player of the Month honors for the NL, leading the league in home runs (10) and runs scored (24) in the opening month of the season while reaching base in every game.
Johnson and Braun will receive engraved trophies for their monthly league honors, which are presented by Budweiser, the official beer sponsor of Major League Baseball.
This is the second Pitcher of the Month honor for Johnson, who also earned the nod in June 2010. He is the fifth Marlins pitcher to win the award, and joins Dontrelle Willis as the only two-time winners.
Johnson wasted no time in getting in a good grove, allowing two runs in 6 2/3 innings against the Mets in his second Opening Day start. He only got better after that, posting three outings of shutout ball over at least seven innings, including a one-hit effort of 7 1/3 innings against the Braves on April 13.
In his last four April starts, covering 28 1/3 innings, he allowed just one earned run. Thus far, Johnson has racked up 39 strikeouts and 11 walks while allowing opponents a .130 batting average -- leaving them duly impressed.
"You see his ERA, that's Bob Gibson stuff right there," said Reds manager Dusty Baker. "He's pitching now more than just throwing. Before, he was more of a power guy. Now, he's a combination of power and finesse. That makes it doubly tough."
While Johnson has been keeping hitters off the basepaths, Braun spent most of the season's first month on them. Including two games in May, Braun has reached base safely in the Brewers' first 28 games, having eclipsed Hall of Famer Robin Yount's franchise record to start a season at 23.
"It means I've been pretty consistent in my at-bats and my approach to the start of the season, and when you get on base every game, you're contributing to winning baseball," said Braun.
A three-time All-Star, Braun earned his third Player of the Month honor. He batted .367 for April with a .457 on-base percentage and a .724 slugging percentage that ranked second in the league. He also racked up 23 RBIs (third in the NL) along with three doubles and a triple to go with his league highs in homers and runs.
Braun had a 3-for-4 game on April 18 to lead the Brewers to a 12-inning win at Philadelphia, delivering the winning run with a sacrifice fly. That began a week in which he batted .480 (12-for-25) with three homers and nine RBIs, to earn NL Player of the Week honors for April 18-25.
Other pitchers receiving votes were Phillies right-hander Roy Halladay (4-1, 2.14 ERA, 47 K, 7 BB), Cardinals right-hander Kyle Lohse (4-1, 1.64 ERA, 24 SO, 5 BB), Rockies closer Huston Street (10 SV, 2.20 ERA) and Pirates closer Joel Hanrahan (1.93 ERA, 8 SV).
Other position players receiving votes were Cardinals right fielder Lance Berkman (.367, 8 HR, 22 RBIs, 23 R, 8 2B), Brewers first baseman Prince Fielder (26 RBIs), Dodgers outfielders Andre Ethier (41 hits, first 26 games of current 28-game hitting streak) and Matt Kemp (.368, 8 SB) and Phillies infielder Placido Polanco (.398, 7 2B, 19 RBIs).
John Schlegel is a national reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.