He has played in Major League Baseball (MLB) for the Minnesota Twins, Boston Red Sox, Baltimore Orioles, Kansas City Royals, Toronto Blue Jays, Oakland Athletics, and Seattle Mariners.

At the University of North Carolina at Greensboro, he was Southern Conference Freshman of the Year, second-team all-conference, and on his all-regional team.

In 2013, he batted .371 vs. left-handed pitching, leading the American League, and ranked third in slugging percentage at .639 (minimum 100 plate appearances).

Through the 2018 season, his 96 home runs placed him 10th on the career all-time list of Jewish major leaguers (directly behind Mike Epstein, and ahead of Joc Pederson), as did his 397 RBIs (tied with Harry Danning, and behind Brad Ausmus).

"[13][14][15][16] In 1996, Valencia pitched for the Boca Raton Babe Ruth League 12-and-under all-star baseball team that won the Florida state championship.

[17] His two key hitting coaches growing up were Bob Molinaro, a family friend who is a former major leaguer and Eastern League manager, and Valencia's mother Mindy.

[18] Valencia attended Spanish River High School and played shortstop for four years on its Sharks baseball team.

He earned South Florida Sun-Sentinel All-County honors as a junior, and was named first team All-Palm Beach County three times and second-team All-State twice.

In his freshman year, Valencia played third base and batted .338 with a .527 slugging percentage and a team-leading 8 home runs.

[10] Homesick for Florida, Valencia sought to transfer to the University of Miami after his freshman year, even though it only offered him a modest scholarship.

UNC-Greensboro initially agreed to release Valencia from his scholarship, but later refused, placing him in jeopardy of losing a year of college eligibility under NCAA Division I rules.

[10][12] During his sophomore year, Valencia played first base for the University of Miami Hurricanes alongside then-third-baseman Ryan Braun.

[19] When Braun left to join the Milwaukee Brewers' farm system in 2005, Valencia replaced him at third base for his junior year, batting .324 with a .475 slugging percentage.

[19][24] Valencia hit .312 with 124 runs batted in (RBIs) in 122 games over two years with the Hurricanes, and played in the College World Series.

Valencia was named a Florida State League All Star, and helped the Miracle capture the FSL 2008 Western Division first half crown.

[38][39][40] Jim Rantz, director of minor leagues for the Twins, said that he expected Valencia would hit for both power and average.

[44] Following the season, Valencia played 31 games of winter ball with the Arizona Fall League's Phoenix Desert Dogs.

"[55] Hector Otero, the Twins scout who signed Valencia and who was the general manager of the Mayagüez club, said: "I think he is a talented player.

"[60] On June 3, Valencia was called up to replace Michael Cuddyer, who had been placed on the bereavement list following the death of his father-in-law.

[62][63] On July 26, Valencia hit a grand slam off reigning AL Cy Young winner Zack Greinke to record his first big league homer.

The feat marked the first time in the 49 years of Twins franchise history that a player's first Major League home run was a grand slam.

[66] Valencia batted .371 vs. left-handed pitching, leading the American League, and ranked third in slugging percentage at .639 (minimum 100 plate appearances).

[66] On July 28, 2014, Valencia was traded to the Toronto Blue Jays for pitcher Liam Hendriks and catcher Erik Kratz.

[85] In the offseason, Valencia won his salary arbitration case against the Blue Jays, and was awarded a one-year contract worth $1.675 million.

[102][103][104] He earned a spot on the Orioles' Opening Day roster, by mid-summer was Baltimore's everyday starting third baseman, and batted .325 after the All Star break.

[105][106][107] On August 2, Valencia became the 8th position player in Baltimore history to pitch, coming in with the Texas Rangers up 17-8, striking out Joey Gallo, the only batter he faced.

[93] On July 2, 2021, Valencia signed with the Long Island Ducks of the Atlantic League of Professional Baseball in order to prepare for the Olympics.

"[117] On June 21, 2021, in preparation for the games (which were postponed to 2021 due to the COVID-19 pandemic), Valencia signed a contract with the Long Island Ducks of the Atlantic League of Professional Baseball.

[119] Commenting on his experience playing for Team Israel, Valencia said: "I loved it.... On Friday nights, we had Shabbat dinner with prayers, toasts, and breaking bread with the boys.

[120][121][122] He played for Team Israel manager Ian Kinsler, and alongside two-time All Star outfielder Joc Pederson, starting pitcher Dean Kremer, and others.