A 2005 graduate of Justin-Siena High School in Napa, California, Wallace earned four varsity baseball letters for head coach Allen Rossi. He helped lead Justin-Siena to a 97–9 record during his prep career, including a perfect 27–0 senior season. He broke nine school records during his prep career and holds single-season school records for walks, runs, hits, RBI, home runs and slugging percentage. Among his numerous accolades, Wallace was named a Collegiate Baseball/Louisville Slugger All-American and 2005 first-team All-State and 2005 California Small SchoolsPlayer of the Year. He was also a four-time All-Marin County Athletic League selection, 2004 and 2005 All-Napa County Offensive Player of the Year.
On July 29, 2010, he was traded again, this time to the Houston Astros, in exchange for minor league outfielder Anthony Gose, who had just been obtained by the Astros from the Phillies as part of a trade for Roy Oswalt. Wallace was sent to the Triple-A affiliate, the Round Rock Express, for one day and did not appear in a game before being called up by the Astros on July 31, 2010 after Lance Berkman was traded to the New York Yankees. Wallace made his MLB debut against the Milwaukee Brewers the same day, and went 0–4. On August 1, he got his first MLB career hit, a single, against Brewers' pitcher Randy Wolf. On September 7 Wallace hit his first MLB career home run off Chicago Cubs pitcher Carlos Silva, tying the game. On August 1, 2011, Wallace was sent back to the Triple-A Oklahoma City RedHawks club. Wallace started the 2012 season with the RedHawks, and was recalled by Houston on June 3 when Carlos Lee was placed on the disabled list. He returned to Oklahoma City on June 17 when Lee was re-activated. Wallace was recalled again on July 30 when Brian Bixler was optioned to Oklahoma City. Wallace began the 2013 season with the Astros. However, due to a slow start in which he batted.042 in 17 games, he was optioned to Oklahoma City on April 18. On June 25, he was called back up to start against the St. Louis Cardinals. On February 6, 2014, the Astros designated Wallace for assignment to make room for Jerome Williams. He was released on March 12.
Return to the minors
Wallace signed a Minor League contract with the Baltimore Orioles on March 23. He played for the Triple-A Norfolk Tides before being traded to the Blue Jays on July 14 for cash considerations. He was assigned to the Triple-A Buffalo Bisons of the International League. On August 24, 2014, Wallace clubbed a walk-offgrand slam in the 12th inning to cap a three home run, six RBI game, as the Bisons rallied for a 10–6 victory over visiting Pawtucket Red Sox. Wallace joined Fernando Martínez and Marco Scutaro as the only Bisons to hit walk-off grand slams at Coca-Cola Field. It was also the sixth three-homer game in franchise history and the first since May 19, 2012, when Vinny Rottino achieved the feat against the Indianapolis Indians.
San Diego Padres
On December 13, 2014, Wallace signed a minor-league contract including an invitation to major-league spring training with the San Diego Padres. On June 19, 2015, the Padres called Wallace up. He finished the season with a.302/.374/.521 slash line in 107 plate appearances for the Padres. The following off season, the Padres and Wallace avoided arbitration by agreeing to a $1 million contract for 2016. Wallace was given the starting third base job when Yangervis Solarte was placed on the disabled list with a hamstring injury. Wallace failed to repeat his 2015 production in 2016, finishing the season with a.189/.309/.318 slash line in 256 plate appearances. He was outrighted off the Padres' 40-man roster after the season. In December 2016, Wallace signed a new minor league contract with the Padres. On April 2, 2017, he was released. Wallace ended his career following the 2017 season.