In 1967, Glasser joined the New York Civil Liberties Union as associate director.

The ACLU website credits Glasser with transforming the American Civil Liberties Union "from a 'mom and pop'-style operation concentrated mainly in a few large cities to a nationwide civil liberties powerhouse.

"[3] At the end of Glasser's directorship the ACLU maintained staffed offices in all fifty states, the District of Columbia, and Puerto Rico; when he became director in 1978, only about half of the states had staffed offices.

[4] Glasser retired in 2001; he was succeeded as executive director of the ACLU by Anthony D. Romero.

In his retired life, Glasser serves as the president of the board of directors of the Drug Policy Alliance.