A native of Maryland, Maxwell was claimed by the Astros after three seasons with the Nationals. Justin led the Astros with 18 homers in 2012 despite a .229 batting average. His production dipped the following season and he was traded to Kansas City for a minor leaguer.

Maxwell closed out his career with the Giants, closing a seven-year career with a .220 batting average, .702 OPS, 41 homers and 113 RBIs.