He played in Major League Baseball (MLB) for the Texas Rangers, Boston Red Sox, San Diego Padres, and Oakland Athletics.

At Amory, he was a 2004 Louisville Slugger All-American after posting a 7–1 win–loss record with a 0.53 earned run average (ERA) as a senior, while also batting .456 and striking out just three times during the season.

[citation needed] The following season, Moreland joined the Class-A Clinton LumberKings of the Midwest League and hit .324 with 37 doubles, four triples, 18 home runs, 99 RBIs and two stolen bases.

[12] On July 29, 2010, Moreland was called up by the Rangers to take the roster spot of Ian Kinsler, who was put on the disabled list.

Moreland had his first major league hit in his first at-bat, a single against Oakland Athletics pitcher Vin Mazzaro.

On October 30, Moreland hit a second inning, three-run home run off of Jonathan Sánchez to put the Rangers ahead 3–0 in Game 3 of the World Series.

On June 21, 2011, Moreland hit his first career walk-off home run off of Enerio del Rosario of the Houston Astros.

On June 9, 2012, Moreland became only the second American League batter—David Ortiz being the first[17]—to hit a home run ball into AT&T Park's McCovey Cove.

[24] On August 25, 2017, Moreland made the second pitching appearance of his career, tossing an inning against the Baltimore Orioles in a 16–3 Red Sox loss; he allowed two hits but no runs, striking out one batter, catcher Caleb Joseph.

[25] During the regular season, Moreland played in 149 games, primarily as Boston's first baseman, batting .246 with 22 home runs and 79 RBIs.

In the postseason, Moreland played in all four games of the ALDS, batting 5-for-13 (.385) as the Red Sox lost to the eventual 2017 World Series champions, the Houston Astros.

In the postseason, Moreland appeared in 11 games, batting 5-for-17 (.294)[28] In Game Four of the World Series, on October 27, 2018, Moreland hit a three-run home run off of the Los Angeles Dodgers' Ryan Madson, which was viewed as a turning point in the series as it put the Red Sox within one run after trailing 0-4, sparking a rally where they eventually won 9–6.

The Red Sox went on to win Game Five 5–1 to capture their 9th championship in franchise history, giving Moreland his first World Series ring.

[34] With the 2020 Red Sox from the delayed start of the season through late August, he appeared in 22 games, batting .328 with eight home runs and 21 RBIs.

He was traded to the San Diego Padres on August 30, 2020, in exchange for minor leaguers Jeisson Rosario and Hudson Potts.

[37] On June 8, 2024, Moreland returned to Fenway Park as one of four former Red Sox to play an exhibition game for the Savannah Bananas barnstorming team.