Freeman was born in Chicago, Illinois. At the age of three she moved with her parents and two brothers to Brooklyn, later moving to New Rochelle, New York and attending New Rochelle High School. Her father was a chemical engineer who had graduated from the Illinois Institute of Technology, and her mother was a mathematics teacher and graduate of the University of Wisconsin. Betty Freeman was a graduate of Wellesley College (1942), where she majored in English literature with a minor in music. She had originally trained to be a concert pianist, practicing six to eight hours per day for twenty years, but eventually, by the mid-1960s, gave up this dream to pursue concert managing. Following her graduation she married and had four children, then later divorced and married the Italian sculptor and painter Franco Assetto (1911-1991), with whom she lived half of each year in Turin.
As of 2003, Freeman had made (since 1961) 432 grants and commissions to 81 composers, often early in their careers. The composers she assisted include Lou Harrison, John Cage, La Monte Young, Christopher Rouse, Philip Glass, Steve Reich, John Adams, Anders Hillborg, Pierre Boulez, Harrison Birtwistle, Virgil Thomson, Helmut Lachenmann, and Kaija Saariaho. John Cage dedicated his Freeman Etudes to her (although she did not commission them), Lou Harrison dedicated his Serenade for Betty Freeman and Franco Assetto to Freeman and her husband, Steve Reich dedicated Variations for Winds, Strings, and Keyboards (1979) and Vermont Counterpoint (1982) to her, and John Adams's opera Nixon in China (1985–87) was dedicated to her. The American gamelan Si Betty, built by Harrison and William Colvig in 1979, was named for Freeman. Bequeathed by Harrison to long-time collaborator and composer Jody Diamond, it has been housed at Harvard University since 2007.
In 1972 Freeman produced a documentary film about the composer and instrument builder Harry Partch, entitled The Dreamer That Remains.
- 1996 - Music People & Others: 99 Photographs From the Contemporary Music World. Issued in conjunction with the exhibition "Betty Freeman: Music People & Others," held at the Royal Festival Hall in London from April 12 to June 16, 1996. Salzburg [Germany]; New York: Festival Press. (Originally published as an exhibition catalog in 1987 by Gabriele Mazzotta (Milan); text by Daniela Palazzoli; text in English and Italian.)
- 1995 - Musical Outsiders: An American Legacy - Harry Partch, Lou Harrison, and Terry Riley. Directed by Michael Blackwood.
- 2005 - Betty Freeman: A Life for the Unknown. Directed by Paul Fenkart. http://www.imdb.com/title/tt0459079/
- "Betty Freeman, art philanthropist and photographer, dies at 87" Los Angeles Times accessed 5 November 2010
- Biography of Betty Freeman at meetthecomposer.org
- Rothstein, Edward (January 28, 1994). "Review/Music; Cello Piece Pays Tribute To Departed Composers". The New York Times. Retrieved May 24, 2015.
- Betty Freeman Papers page
- Betty Freeman Papers page
- Death notice from Slipped Disc, an ARTSJOURNAL weblog