Slowey drew little attention from Division I schools and ended up attending Winthrop University on an academic scholarship after scoring a 1420 on his SAT. He went on to be named as a third-team All-American by Baseball America in 2005 when he had 14-2 record with 126 strikeouts, only 13 walks issued, and a 2.16 ERA. In his three seasons at Winthrop, he set school records with 331 strikeouts and 29 wins.
Slowey ascended rapidly through the Twins minor league system and after failing to make the team as a dark horse candidate out of spring training, he began the 2007 season with the Triple-A Rochester Red Wings. After a 6-2 start 1.54 ERA, 57 strikeouts, and 5 walks for the Red Wings, he was called up to the Twins and made his major league debut on June 1, 2007 as a replacement for struggling Ramón Ortiz in the starting rotation. In his first major league start against the Oakland Athletics, Slowey received a no decision in a Twins 3-2 win. He gave up one run, five hits, struck out three, and walked two in six complete innings. The lone run came off of a solo home run in the sixth inning by the A's Eric Chavez. A highlight of the start occurred early in the game when in the first inning, Slowey showed excellent poise in working out of a bases loaded jam. In his second start, on June 6, 2007, Slowey earned the first win of his MLB career. The win came against the Los Angeles Angels of Anaheim. He pitched five innings giving up five runs, four of them earned, striking out two, and walking none as the Twins won 8-5. After an excellent start against the Atlanta Braves on June 12, 2007, in which he gave up 2 earned runs, Slowey began to struggle through his remaining starts. On July 5, 2007, after giving up 5 earned runs in 3 innings against the New York Yankees, Slowey was optioned back to the Triple-A Rochester Red Wings, exchanging his roster spot with Carmen Cali.
2008 season
Slowey pitched 10.2 innings for the Minnesota Twins in spring training, posting a 2-1 record and 5.90 ERA, earning him a spot on the starting rotation. On April 11, 2008, he was placed on the 15-day DL. On May 8, 2008, he was activated from the DL. On May 29, 2008, he pitched his first MLB complete game. In that game against the Kansas City Royals, he was one out away from a shutout as well; however, he up gave an RBI double. In his 101st pitch of the night, he retired the next batter and finished the night with a victory after nine innings of work. On June 29, 2008, he pitched his first big league complete shutout game against the Milwaukee Brewers. At the end of the 2008 season, he had a 12-11 record with a 3.99 ERA, 24 walks, and 123 strikeouts. He went 0-2 on 33% of all batters he faced, the highest percentage in the majors.
2009 season
Slowey posted a very impressive 10-3 record. However, he posted an ERA of 4.86, and a WHIP of 1.412. Slowey's season was cut short when he was placed on the disabled list for a strained right wrist on July 4. Tests revealed that a pre-existing bone fragment was responsible for the aggravation. Slowey had season-ending surgery on his wrist in late July.
2010 season
Despite having wrist surgery, he was able to start the season in the Twins rotation, winning in his first start of the year against the Los Angeles Angels. On July 1, 2010 he left a game against the Detroit Tigers after he was hit in the ankle by a batted ball, but did not miss any time on the mound. On August 8, 2010, Slowey missed a start against the Chicago White Sox due to elbow soreness. On August 15, 2010 he pitched 7 no-hit innings against the Oakland Athletics before being removed in the top of the eighth for Jon Rauch. Rauch retired the first batter he faced before giving up a double to Cliff Pennington. Addressing the questionable move, manager Ron Gardenhire said, "It's the way it is. It's sad. I'd be booing too because I want to see a no-hitter, but I also know I'm responsible for this guy's arm", as he alluded to the elbow tendinitis that caused Slowey to miss his last start. Slowey had thrown 106 pitches through his seven innings. As of August 16, 2010 he was 11-5 with a 4.22 ERA. He ended the season going 13-6 with a 4.45 ERA in a career high 30 games.
2011 season
In Spring Training 2011, Slowey was given a chance to win a spot in the Twins starting rotation, but he was unsuccessful. He began the 2011 season in the bullpen. His 2011 was abysmal as he did not record a win in 8 starts, while also making 6 relief appearances. He lost all 8 starts he pitched in, going 0-8 while allowing 44 runs in 59.1 innings pitched. This season marked Slowey's last with the team.
On December 6, 2011 Slowey was traded to the Colorado Rockies in exchange for a player to be named later. Then, just 6 days later, Slowey agreed to a one-year deal to avoid arbitration.
Slowey was traded to the Cleveland Indians on January 20, 2012 in exchange for Zach Putnam. He was optioned to the Triple-A Columbus Clippers and subsequently spent the entire season on the minor-league disabled list. Slowey was outrighted to Columbus and removed from the Indians' 40-man roster on October 31, 2012. He subsequently elected to become a free agent.
Miami Marlins
Slowey signed a Minor league deal with the Marlins as a non roster invitee with an invitation to spring training. Slowey had a strong spring training, pitching to a 2.41 ERA and a WHIP of 1.13 in 6 games. Due to his strong performance, Slowey made the team and was named their #3 starter to start the season.
2013 season
Slowey started the 2013 season with several quality starts, and was the Marlins' best statistical starting pitcher in April. Unfortunately, he lacked the run support to earn a victory until May 5, 2013, against the Philadelphia Phillies. It was Slowey's first win at the major league level since September 2010, snapping a 15-start winless streak. On June 8, Slowey got the win in a 20 inning game against the Mets, pitching 7 scoreless innings. After his start against Milwaukee on June 12, he was demoted to the bullpen and was replaced in the rotation by Nathan Eovaldi. After Tom Koehler was optioned and Ricky Nolasco was traded, Slowey got the start on July 8 against the Braves, pitching 5 scoreless innings. After the break, Koehler was recalled and Slowey returned to the bullpen. On July 28, Slowey was placed on the disabled list and missed the rest of the season due to a right flexor strain. In 20 games for the Marlins, he went 3-6 with a 4.11 ERA, striking out 76 in 92 innings.
On December 22, 2014, Slowey signed a minor league deal with an invitation to spring training with the Philadelphia Phillies. where he competed with several other pitchers for a spot in the back of the Phillies' starting rotation. He was released on March 31, 2015. On June 2, 2015, Slowey announced his retirement from baseball. He has taken a position in the Major League Baseball Player's Association as a special assistant to Tony Clark, the executive director.
Pitches
Slowey was considered to be a control pitcher and his repertoire included a low 90s fastball considered to be his best pitch, a good changeup, a good slow curveball, and a tight slider. He was known for his exceptional control and command of the strike zone and was often compared to former Minnesota Twins pitcher Brad Radke, due to his excellent control. Slowey's delivery was much simpler than Radke's, however, mainly due to the absence of Radke's high leg kick.
