The 16-year-old forward has rapidly progressed through United's academy, and has been rewarded with a pro contract.
The 6-foot-0 Seaton impressed with United's U15 and U16 teams last season, before making an appearance with the reserve team at the end of 2012.
“Michael has made big strides in a short amount of time in our academy system and he is ready to take the next step,” said D.C. United general manager Dave Kasper. “As an attacking player, Michael has an excellent work rate and is a real handful for opposing defenses."
Seaton was born in Jamaica, and is a native of Capitol Heights, Maryland. He has represented Jamaica at the U17 level.