Snowden's leaks to Greenwald and others in 2013 prompted one of the most intense debates over press freedom in recent memory.
Snowden remains in Moscow, where he has been granted asylum by the Russian government.
The Freedom of the Press Foundation was launched in 2012 with the intention of aiding investigative journalism and combating government secrecy. Besides Ellsberg and Greenwald, other board members include John Cusack, Laura Poitras and Xeni Jardin.
CORRECTION: An earlier version of this story misspelled Xeni Jardin's name.