Aaron Harang participant of 2006 Major League Baseball season
In the 2006 season, Harang pitched on Opening Day for the Reds on April 3 against the Chicago Cubs and allowed 9 runs (6 earned) over 5 innings. In his third start of the season, 11 days after Opening Day, Harang pitched 7 shutout innings against the St. Louis Cardinals, who were starting 2005 Cy Young Award winner Chris Carpenter. Harang would give up 4 hits, get 4 strikeouts, and also had the only RBI of the game as the Reds won 1–0. Harang also pitched a complete game shutout against the Milwaukee Brewers on April 23, allowing five hits as the Reds won 11–0.
In the 2006 season, Harang led the National League in complete games with six and strikeouts with 216, surpassing Jake Peavy's strikeout total of 215 in his final regular season game. Harang was also the most consistent pitcher on the 2006 Reds staff. Harang was only the ninth pitcher since 1960 to lead the National League in both wins and strikeouts (it has occurred 12 times in baseball history). However, he did not receive any votes for the National League Cy Young Award (Brandon Webb won the award in 2006). All previous pitchers that led the National League in both categories have won the award.On February 6, 2007, Harang signed a four-year, $36.5 million contract with the Cincinnati Reds. On July 23, 2007, Harang threw ten innings for the Reds (throwing 121 pitches), becoming the first Reds pitcher to do so since 1989. However, he received a no-decision because the Reds did not win the game until the 12th inning. On September 3, 2007, he became the victim of the 3,000th strikeout recorded by the New York Mets' Pedro Martínez. Harang ended the season with an NL-leading 4.19 strikeout-to-walk ratio and 12 wild pitches.
In 2008, he led the major in home runs given up at home, with 19.In the second inning of a game at Wrigley Field in Chicago against the Cubs on July 24, 2009, Harang hit his first career home run, a three-run shot to left field off of pitcher Randy Wells. He missed the end of the 2009 MLB season after undergoing an emergency appendectomy. He ended the year with a 4.21 ERA, 1.41 WHIP and 6–14 record.
On September 10, 2010, it was announced that Harang would be sent to the bullpen due to ineffectiveness (5.32 ERA) and having been on the DL for two months due to back spasms. In a ceremonial "goodbye", he started the final game of the season against the Brewers, but exited after three innings with a blister on his finger. Harang was left off the Reds 2010 playoff roster. On November 3, 2010, the Reds bought Harang out of his 2011 contract option, making him a free agent.