The 28-year-old native of Brazil follows teammate Christian Gomez as the second straight D.C. United player to win the MVP, and the third United player ever so honored.
Marco Etcheverry was named MVP in 1998.
Emilio scored a league-high 20 goals this season, which led to the Golden Boot Award, given annually to the top goal-scorer.
In his first MLS season, he helped lead United to a 16-7-7 record and their second consecutive Supporters' Shield as the league's winningest team.
He was the first MLS player to score at least 20 goals in one season since 2002, when FC Dallas forward Carlos Ruiz scored 24 for the Los Angeles Galaxy and Taylor Twellman scored 23 for the New England Revolution.