He played in Major League Baseball (MLB) for the Washington Nationals, Houston Astros, Kansas City Royals, and San Francisco Giants.

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.

On September 30, Maxwell hit a two-out full count walk off grand slam off of Francisco Rodriguez of the New York Mets on Fan Appreciation Day, the Nationals' last home game of the season.

[12] On February 2, 2011 the Nationals traded Maxwell to the New York Yankees for minor league pitcher Adam Olbrychowski.

[21] 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.

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

From August 31 to September 3, 2019, Maxwell made his debut as a broadcaster, serving as a substitute studio analyst on the Nats Xtra shows that aired before and after Washington Nationals games on the Mid-Atlantic Sports Network.

[27] Maxwell enrolled at the University of Maryland School of Dentistry in 2019 and graduated as a Doctor of Dental Surgery in 2022.

[28] As of 2025, he operates a dental practice called Major League Smiles in Ellicott City, Maryland.