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.