Green is known as an activist for the legal protection, medical access, safety, civil rights and dignity of transgender and transsexual people. He has published several essays and articles, and writes a column for PlanetOut.com. He has appeared in eight documentary films.

He chairs the board of Gender Education and Advocacy, a non-profit educational organization, and serves on the boards of the Transgender Law and Policy Institute and the World Professional Association for Transgender Health. He is also a board member of the Equality Project and an advisory board member of the National Center for Transgender Equality. He was the leader of FTM International from March 1991 to August 1999 and a member of the Human Rights Campaign Business Council until late 2007, when he resigned over the organisation's stance on transgender inclusion in the Employment Non-Discrimination Act.

Writings

He is the author of Becoming a Visible Man, which received the 2004 Sylvia Rivera Award for Best Book in Transgender Studies from the Center for Lesbian and Gay Studies. The book combines two strands: autobiographical writing about Green's transition from living as a lesbian woman to living as a heterosexual man, as well as broader commentary about the status of transsexual men in society. It was also a finalist for a 2004 Lambda Literary Award.