After the minor league season ended, the Nationals promoted Maxwell to the major leagues, though he "was told not to expect much from his first month in the majors." On September 5, he made his debut, as pinch hitter, and flew out to the warning track. Six days later, in his third pinch hitting appearance, Maxwell recorded his first career base hit, a pinch-hit grand slam off an 0–2 pitch from Chris Seddon, of the Florida Marlins. After the 2007 regular season, Maxwell played for the Peoria Javelinas in the Arizona Fall League.