The Oscar winner broke out into a song from the hip-hop musical, centered on the life of Alexander Hamilton, while making a speech at the Women in the World Summit in New York City on Friday.
Streep, 66, put her own spin on "The Room Where it Happens," even doing a little choreography with her hands.
"All of a sudden we're in the room where it happens ... Women are suddenly in the room where it happens," she sang as the audience cheered and applauded.
"I couldn't resist that," Streep added.
Actor Leslie Odom, Jr., who portrays former Vice President Aaron Burr in "Hamilton," sings the song in the second act. The original lyrics are: "I want to be in the room where it happens."