Maxwell was drafted out of Sherwood High School by the Baltimore Orioles in the 43rd round (1279th overall) of the 2001 Major League Baseball Draft, but opted instead to attend college at the University of Maryland. In 2003, he played collegiate summer baseball with the Bourne Braves of the Cape Cod Baseball League, and returned to the league in 2004 to play for the Cotuit Kettleers. He was drafted, again, in 2004 by the Texas Rangers in the 10th round (291st overall), but declined, and the following year by the Washington Nationals in the 4th round (114th overall). He signed and played most of 2006 for the Vermont Lake Monsters, the Nationals Short-Season A team.

In 2007, he split his time between Low-A Hagerstown, and High-A Potomac, where, he combined to hit .281 with 27 home runs, 83 RBI and 35 stolen bases, the only player in Minor League Baseball to record at least 25 doubles, 25 home runs and 25 stolen bases in 2007.”

Maxwell was assigned to the Harrisburg Senators of the Double-A Eastern League in 2008 after hitting .280 in 13 spring training games for Washington, but missed most of the year with a fractured wrist suffered while diving for a flyball in the outfield.

Maxwell split time with the AAA Syracuse Chiefs of the International League and the Nationals in 2010. On September 15, Maxwell hit a grand slam in the 2nd inning off of Mike Minor of the Atlanta Braves giving him three grand slams in four career at bats with the bases loaded. In September, Maxwell sat out two games with a minor thumb injury suffered on September 18. He returned September 21 against the Houston Astros. Maxwell underwent Tommy John surgery after the season.

On February 2, 2011 the Nationals traded Maxwell to the New York Yankees for minor league pitcher Adam Olbrychowski. Maxwell began the 2011 season with the Triple-A Scranton/Wilkes-Barre Yankees, but his season ended prematurely due to a torn labrum. The Yankees designated Maxwell for assignment at the end of spring training in 2012.

Maxwell was traded to the Kansas City Royals for Kyle Smith on July 31, 2013. He hit a walk-off grand slam on September 22, 2013 against the Texas Rangers. He was designated for assignment on May 16, 2014. After being re-added to the roster, he was designated for assignment again on June 30, 2014. Maxwell elected free agency in October 2014.

Entering the 2015 spring training as a non-roster hopeful for the San Francisco Giants, Maxwell hit for power and a .300+ batting average, which earned him a contract for the 2015 season. He was designated for assignment on September 1, 2015.

On November 30, 2015, Maxwell signed a minor league deal with the Miami Marlins. He was released on March 29, 2016.

On April 1, 2016, Maxwell signed a minor league deal with the Boston Red Sox.

On July 6, 2016, Maxwell signed with Lotte Giants of the Korea Baseball Organization for the rest of 2016 season.