He played in Major League Baseball (MLB) for the Minnesota Twins, Chicago Cubs, Texas Rangers and Los Angeles Dodgers.

In 2009, Baker logged a career-high 200 innings and started the American League (AL) tiebreaker game against the Detroit Tigers which the Twins won to advance to the postseason.

Signed by the Los Angeles Dodgers, he started two games for them, the last appearances of his major league career.

He was selected to the All-State team his senior year and played college baseball at Oklahoma State University.

In 2004, he played for the Class A-Advanced Fort Myers Miracle, Double-A New Britain Rock Cats, and Triple-A Rochester Red Wings, where he would spend the rest of his minor league career outside of rehab assignments until 2014.

[8] Baker did not wind up starting, making his MLB debut by pitching one scoreless inning out of the bullpen in an 8–1 victory over the Tampa Bay Devil Rays on May 7.

Though he was expected to get sent back to Rochester, Twins' manager Ron Gardenhire had praise for him, saying after the game, "We think we have a quality major leaguer ready to go, and he kind of proved that theory again.

[10][13] Baker finished his rookie year with a record of 3–3 and an earned run average (ERA) of 3.35 in 10 games (nine starts).

[15] Baker ended up spending nearly the entire second half with the Rochester Red Wings, making only a handful of starts after the demotion.

[16][17] In his first start of the season, on May 19, he pitched into the ninth inning, allowing two runs in a 5–2 victory over the Milwaukee Brewers.

[16] On July 26, after scuffling in several starts, he struck out a career-high nine hitters over seven innings in a 12-inning, 2–1 victory over the Toronto Blue Jays.

[20] On August 31, Baker took a perfect game into the ninth inning against the Kansas City Royals at the Hubert H. Humphrey Metrodome during the second game of a doubleheader, but lost his bid for perfection when he issued a walk to the first batter he faced in the ninth, John Buck.

The second hitter after Buck that he faced, Mike Sweeney, hit a single, ending Baker's bid for a no-hitter.

[24] Baker picked up his first career hit against Josh Banks on June 26 and earned the win in a 4–3 victory over the San Diego Padres.

[34] Baker began trying to stand taller in his delivery, and on June 4 he struck out a career-high 10 batters in an 11–3 victory over the Indians.

[36] After sitting seven games out of the AL Central lead on September 6, the Twins forced a tiebreaker with the Tigers, and Baker made the start.

[37] He led the Twins with 15 wins, 162 strikeouts, and finished second on the team behind Nick Blackburn with a 4.37 ERA, while pitching a career high 200 innings.

However, the Twins were swept in three games in the AL Division Series (ALDS) against the Yankees, preventing Baker from making any playoff appearances.

[1] Baker started on Opening Day for the Twins to kick off the 2010 season against the Angels but allowed four earned runs in 4+2⁄3 innings, taking the loss in a 6–3 defeat.

[41] He picked up his 50th career win on July 2, allowing one earned run in seven innings in a 2–1 victory over the Tampa Bay Rays.

[45] He made his playoff debut in Game 3 of the ALDS, allowing one run in 2+1⁄3 innings as the Twins were again swept by the Yankees.

[46] Baker had to compete with Kevin Slowey for the starting rotation in 2011, but he won the competition and entered the season as the Twins' No.

His ERA at the end of July was 2.86, and he made two starts in August before spending much of the rest of the season on the disabled list with an injured elbow.

[1] Baker was the Twins only starting pitcher to have a winning record in 2011, and he led the team in ERA, strikeouts (123), and WHIP (1.17).

[59][60] After posting a 6.75 ERA in four Spring training starts with the Mariners and refusing a minor league assignment, Baker was released on March 24.

[63] He was designated for assignment after throwing 5+1⁄3 innings of relief in a game, with the Rangers needing more-rested arms in their bullpen, but he was soon recalled.

[73] The Dodgers purchased his contract and called him up to the Majors to make a spot start against the San Diego Padres on April 26.

The fastball was his main pitch, which he threw over 60 percent of the time; it had an average velocity in the high nineties for much of his career.

After Baker's return in 2013, his average fastball velocity had dropped to the high eighties, and he stopped throwing the curveball after the 2013 season.

[78] Baker has been a good control pitcher throughout his career, finishing in the top 10 in the American League in strikeout-to-walk ratio three times.