He currently serves on the Administrative Committee of anti-war coalition United for Peace and Justice, the Board of Directors of Peace Action and the Advisory Board of website Occupation watch. In 2002 he ran as the Green Party candidate for governor of Texas.
Mahajan has been particularly involved in campaigning around issues relating to Iraq. He was an opponent of the sanctions regime imposed on Iraq under the auspices of the UN during the 1990s. He was actively involved in opposition to the 2003 invasion of Iraq and has remained an outspoken critic of the ongoing occupation. He has travelled to Iraq twice and reported from Fallujah during the siege in the month of April 2004.