Maynor began at Hoke County High School in Raeford, then transferred to Westover High School in neighboring Fayetteville for his senior year to play alongside his friend and AAU teammate De’shaune Griffin. Maynor led the team to the North Carolina state championship game, scoring 25 point in a loss to North Mecklenburg High School on March 14, 2005. For his outstanding performance during the season Maynor was named to the 2004/05 North Carolina All State Basketball team by the sports website NCPreps.com.

On March 15, 2007, Maynor scored 22 points, including the game-winning shot, in VCU’s victory over Duke in the first round of the 2007 NCAA Men’s Division I Basketball Tournament. Maynor’s last-minute heroics are also what helped VCU to overcome George Mason in the 2007 Colonial Athletic Association (CAA) championship game.

During the 2008–09 season, Eric Maynor became VCU’s all-time leader in assists and in made free-throws. On February 28, 2009, Maynor became the leading scorer in VCU history with a floater against Georgia State. As of March 10, 2009, he had scored a school record 1,929 points. Maynor also led VCU to a second CAA title during his career, scoring 25 points in a 71–50 victory over George Mason on March 9, 2009, at the Richmond Coliseum. The Rams went on to the 2009 NCAA Tournament but lost to UCLA when Maynor missed a buzzer-beater to win the game.

Maynor was drafted 20th overall by the Utah Jazz in the 2009 NBA draft. He became the first VCU player ever selected in the first round of the NBA draft.

Maynor signed a two-year contract with the Jazz on July 1, 2009, and made $1.3 million in his rookie season. Although he was to back up Deron Williams, Maynor had a positive outlook on the situation. When asked in an interview with RealCollegeBasketball.com what he thought about coming off the bench in Utah, Maynor replied, “Feel real good about it… I’m getting a chance to learn from some of the best”.

On December 22, 2009, Maynor, along with Matt Harpring, was traded to the Oklahoma City Thunder for the rights to Peter Fehse. According to a statement made by Jazz General Manager Kevin O’Connor at the time of the deal, the trade of Maynor along with the $6.5 million contract of the injured power forward Harpring was made for financial reasons, in an effort to reduce the team’s liability under the NBA’s punitive “luxury tax” on teams with excessive salaries.

On January 7, 2012, the Thunder reported that Maynor had torn his right anterior cruciate ligament (ACL) in the fourth quarter of Oklahoma City’s 98–95 win over the Houston Rockets and would miss the remainder of the season. Without Maynor the Thunder reached the 2012 NBA Finals, but lost in five games to the Miami Heat.

In a deal concluded just 30 minutes before the noon trade deadline on February 21, 2013, Maynor was traded to the Portland Trail Blazers for the NBA rights to Greek player Giorgos Printezis. Maynor was averaging just 2.8 points and 2.0 assists in an average of about 10.6 minutes per game playing for the Thunder and had fallen to number three on the team’s depth chart for point guards, with second-year player Reggie Jackson emerging to capture most of the team’s backup PG minutes. The Blazers were forced to waive reserve point guard Ronnie Price to make room on the team’s 15-man roster for Maynor.

On July 10, 2013, Maynor signed with the Washington Wizards.

On February 20, 2014, Maynor was traded to the Philadelphia 76ers in a three-team trade involving the Nuggets and the Wizards. On March 17, 2014, he was waived by the 76ers.

On January 14, 2015, Maynor signed a contract with Pallacanestro Varese of Italy for the rest of the 2014–15 Lega Basket Serie A season.

On July 23, 2015, he signed a one-year contract with the Russian club Nizhny Novgorod.

On July 27, 2016, Maynor returned to Pallacanestro Varese, signing a contract for the 2016–17 season.

On November 20, 2017, Maynor signed with Italian club Orlandina Basket for the rest of the 2017–18 season.

In 2017, Maynor participated in The Basketball Tournament for Ram Nation, a team of VCU alumni. Maynor averaged 13.5 PPG, 7.3 APG, and 5.5 RPG to help Ram Nation reach the Elite 8. In the Elite 8, Ram Nation lost a close game to the eventual tournament champs, Overseas Elite. The Basketball Tournament is an annual $2 million winner-take-all tournament broadcast on ESPN.

In September 2019, Maynor was named Assistant Coach of the Oklahoma City Blue.