Feliz was called up to the majors for the first time on August 2, 2009. He made his debut on August 3, striking out four in two scoreless innings. He finished the season with a 1–0 record and a 1.74 earned run average in 20 games, with 39 strikeouts and two saves in 31 innings pitched.
2010
After two blown saves by Frank Francisco to start the 2010 baseball season, Feliz replaced him as the Rangers' closer. On July 4, 2010, he was named to his first MLB All-Star Game. He was accompanied by teammates Vladimir Guerrero, Josh Hamilton, Ian Kinsler, Elvis Andrus, and the newly acquired Cliff Lee. However, Feliz did not pitch during the game. On September 1, 2010, Feliz threw a fastball recorded at 103.4 mph, currently the 3rd fastest recorded pitch that has ever been thrown. On September 25, 2010, he earned his 38th save of the season, breaking the single-season record for saves by a rookie. He would go on to finish the season with 40. The previous record was held by Kazuhiro Sasaki of the Seattle Mariners, with 37 in 2000. During Game 6 of the 2010 American League Championship Series against the New York Yankees, Feliz got the final three outs in the 9th inning and sent the Rangers to the World Series for the first time in franchise history. On October 30, 2010, he went three up, three down to close a 4–2 Rangers win in Game 3 of the World Series, making him the second youngest player to record a save in the World Series. The Rangers lost the World Series to the San Francisco Giants in 5 games. On November 15, 2010, Feliz was awarded the 2010 American League Rookie of the Year Award. He was also named the closer on Baseball America's 2010 All-Rookie Team and the ToppsMajor League Rookie All-Star Team.
2011
In 2011, Feliz was 2–3 with a 2.74 ERA and 32 saves. During Game 6 of the 2011 World Series, with two outs, two strikes, and two runners on, Feliz blew a save as he surrendered a 2-run triple to David Freese, who would then homer later to seal a Cardinals 10-9 win in the 11th inning. The Rangers then lost their second straight World Series appearance after losing Game 7 to the Cardinals 6-2.
2012
With the addition of veteran closer Joe Nathan, the Rangers transitioned Feliz into the starting rotation for the 2012 season. His first start came on April 10 against the Seattle Mariners. He pitched 7 shutout innings, only giving up 4 hits and 2 walks with 4 strikeouts in a 1-0 victory. On May 21, 2012, Feliz was placed on the 60-day disabled list due to a sprained UCL. After several rehab appearances Feliz underwent Tommy John surgery on August 1, 2012. In 8 games, he went 3-1 with a 3.16 ERA during his injury-shortened 2012 year.
2013
Feliz began the 2013 season on the 60-day disabled list still recovering from Tommy John surgery. On September 1, he was activated from the disabled list with the intention to use him in low-leverage situations. He pitched later that night in a lost cause to the Minnesota Twins, pitching 1 2/3 innings of relief. Feliz finished the season with only six appearances in which he did not give up a run and struck-out four.
2014
Feliz opened the season as the Rangers set-up man. He became the closer again after Joakim Soria was traded. He saved 13 games by the end of the season for the Rangers despite only appearing in 30 games due to injury.
2015
Feliz was designated for assignment on July 3, 2015 after posting underwhelming stats and being on the DL for the third straight season. He was outrighted off the roster on July 9 and elected to become a free agent.
Detroit Tigers
On July 11, 2015, Feliz signed a one-year contract with the Detroit Tigers. He made his debut for the Tigers later that day, pitching a scoreless ninth inning, allowing one hit and one strikeout. After the season, he was non tendered, making him a free agent.
Pittsburgh Pirates
On January 6, 2016, Feliz signed a one-year, $3.9 million contract with the Pittsburgh Pirates.
Milwaukee Brewers
On January 19, 2017, Feliz signed a one-year contract with the Milwaukee Brewers. He was designated for assignment on June 14, and released on June 19.
Kansas City Royals
On June 22, 2017, Feliz was signed by the Kansas City Royals. He was released on September 1.
