He was a star player both in high school & at Stanford where he got to the College World Series as a freshman. He also played for Team USA in 2004 winning the University Championship.
He was drafted in the first round (the 19th pick overall) by the Texas Rangers in 2005. He proved to labeled a slugger early on as he hit 21 HRs at A ball in 2006. In 2007 he totaled 30 HRs between A ball plus Bakersfield & AA Frisco.
In 2008 he was traded to the Philadelphia Phillies organization for Greg Golson. He got to the AAA level, hitting 16 HRs with 30 doubles at Lehigh Valley.
He debuted with the Phillies in 2009 hitting a three run HR against the AL New York team, in his first game. That day the FOX cameras wrongly identified a man in the stands as his father, Mayberry Sr. John Jr. got a kick out of the whole mistaken identity thing.

Trivia: That year Mayberry made headlines when he tried to use his agent to get a date with Bronx born, Albanian actress; Antoinette Nikprelaj, who played a mermaid in the Pirates of the Caribbean movie. What he & the agent did not know was that she was married and had a daughter.
In 2012 he saw action in 149 games, hitting 14 HRs with career highs in doubles (24) & hits (108) batting .245. He struck out 111 times that season & 90 times the next year in 353 at bats. 2013 was his last year as a regular utility man, as he fell to a .227 average with 11 HRs.

In 2014 he was traded from the lowly Phillies to the Toronto Blue Jays for a minor leaguer. There he played just 15 games batting .208 & was let go to free agency.
In the off season he was signed by the New York Mets. Mayberry would be used by Manager Terry Collins at first base, the outfield & as a pinch hitter. He made his Mets debut on Opening Day, going 0-1 as a pinch hitter in the 3-1 win in Washington. On April 10th he got his first start & hit his first Mets HR a solo shot in a 5-3 Mets loss to the Braves in Atlanta.
Over the next month he was in a major drought seeing his average fall to .103. Then on May 14th he had an two run single at Wrigley Field. On May 18th he had his biggest Mets hit, it came as a pinch hitter in the bottom of the 14th inning of a 1-1 tie with the St. Louis Cards at Citi Field. Mayberry singled home the winning run as Eric Campbell scored the walk off run.
June seemed to be better for Mayberry as he had a big four hit day in Arizona, driving in two of the Mets six runs, including his second HR of the season in the 6-2 win. That week he saw his average climb back up over .200 as well. On June 12th he hit a two run HR helping Bartolo Colon beat the Atlanta Braves 5-3 at Citi Field.
At the end of July Mayberry was hitting .164 with 3 HRs 9 RBIs & was designated for assignment.
After his release from the Mets he was signed but released by the Chicago White Sox & Detroit Tigers. In his seven year career he played in 574 games batting .235 with 326 hits 56 HRs 83 doubles 180 RBIs & 172 runs scored. He played 404 outfield games 75 games at First base & 5 games as a DH.