Born in Washington, D.C., Chasanow received a B.A. from Rutgers University in 1970 and a J.D. from Stanford Law School in 1974. She was a law clerk, Hon. David L. Cahoon, Montgomery County Circuit Court, Maryland from 1974 to 1975, and was in private practice in Washington, D.C. in 1975. She was an Assistant state attorney general in the Office of the Maryland Attorney General from 1975 to 1987, and was chief of the Criminal Appeals Division from 1979 to 1987. She was a United States Magistrate Judge for the U.S. District Court for the District of Maryland from 1987 to 1993.