A makeup date has yet to be announced.
The Marlins won the opener of the scheduled three-game series 3-2 on Monday -- just their second win in their last 14 games in Washington.
Right-hander Henderson Alvarez was scheduled to start Tuesday's game for Miami against Nationals righty Blake Treinen.
Treinen, a 25-year-old rookie, will have to wait at least one more turn to get his first major league win.
Showers and thunderstorms moved into the Washington, D.C., area ahead of the scheduled 7:05 p.m. EDT start time and more were forecast through the night.