He played in Major League Baseball (MLB) for the Colorado Rockies, Cleveland Indians and Baltimore Orioles.

Jimenez earned his 100th MLB career victory on September 22, 2015, as a member of the Baltimore Orioles, while pitching against the Washington Nationals.

At 16 years old, he was offered a contract by the New York Mets but his mother said that he could not sign because he needed to finish high school.

[2] He signed with the Colorado Rockies on April 25, 2001,[3] for $50,000 in part because they allowed him to skip training to finish high school.

He came in as a relief pitcher for the Colorado Rockies during the eighth inning of an 11–4 home loss to the Los Angeles Dodgers.

He would make his first MLB start on October 1 against the Chicago Cubs on the road, which was the last game of the regular season.

On September 5, he gained the distinction of giving up Barry Bonds's 762nd and final career home run.

He started the game and pitched six innings, allowing three hits and one earned run, as part of a 2–1 victory (the win gave the Rockies a series sweep over the Phillies).

On March 10, he set a single-start strikeout record, fanning 10 of the 13 batters he faced during his 65-pitch, four-inning performance in Round One against the Netherlands.

[15] On April 17, 2010, Jiménez no-hit the Atlanta Braves 4–0 at Turner Field, the first no-hitter in the history of the franchise.

The no-hitter was preserved by a diving catch in center field by Dexter Fowler in the bottom of the seventh inning.

[18] Jiménez was only the second pitcher in MLB history to throw a no-hitter and notch five wins in the month of April.

On July 12, 2010, Jiménez was named the starting pitcher for the National League All-Star team ahead of fellow NL aces Tim Lincecum, Roy Halladay, and Adam Wainwright.

On July 31, 2011, Jiménez was traded to the Cleveland Indians in exchange for Alex White, Joe Gardner, Matt McBride and Drew Pomeranz.

[26] Tom Verducci wrote in Sports Illustrated shortly before the trade "Jimenez has terrific stuff, a powerful frame and the work ethic of a blast furnace" but was working an alarming number of innings in high altitude conditions and putting strain on the Rockies' ace.

"[28] On April 2, 2012, Jiménez was suspended five games by MLB for hitting former teammate Troy Tulowitzki with a pitch on the elbow the previous day.

[30] In a start against the Toronto Blue Jays on July 14, Jiménez struggled with his command and had his shortest outing on the season, being pulled after 2+1⁄3 innings,[31] and matched a career-high 8 earned runs.

Jiménez elected to opt out of the final year of his contract with the Indians and became a free agent on November 1, 2013.

[33][34][35] In his first start with the Orioles, Jimenez threw six innings against the Red Sox, getting tagged for four runs and a loss.

On April 11, 2015, in his first start of the season, Jimenez pitched 7 shutout innings, against the Toronto Blue Jays.

On April 17, 2015, in a start against the Boston Red Sox, Jiménez was ejected for the first time in his career by home plate umpire Jordan Baker.

Baker deemed the hit by pitch intentional, after Sandoval had slid into second baseman Jonathan Schoop, to break up a double play.

On February 5, 2020, Jimenez signed a minor league deal with the Colorado Rockies and was invited to spring training.

In 2008, Jiménez posted a very robust ground-ball percentage of 54.4%,[41] a testament to this pitch's effectiveness and making him an ideal pitcher for Coors Field, a ballpark known for extra-base hits.

Jiménez was known to throw a split-finger fastball and an occasional forkball, having deceptive downward movement in the 85–88 mph range.

This pitch fooled batters with an unusually sharp, late break and was used second most in frequency behind his four-seam fastball.