Greenwald practiced law in the litigation department at
Wachtell, Lipton, Rosen & Katz from 1994 to 1995. In 1996, he co-founded his own litigation firm, Greenwald Christoph & Holland (later renamed Greenwald Christoph PC), where he litigated cases concerning issues of U.S. constitutional law and civil rights.
[7][8] He worked
pro bono much of the time, and his cases included representing white supremacist
Matthew Hale in Illinois and the neo-nazi
National Alliance.