Oscar Rosales Castaneda was born in Guadalajara, Mexico. At an early age, his parents immigrated to the United States and later settled in the Yakima Valley. At A.C. Davis High School, in Yakima, WA, Rosales became involved in MEChA and started to develop a passion for social justice. After graduating, he moved to Seattle to attend the University of Washington.
At the University of Washington, Rosales continued to be involved in MEChA but also joined and collaborated with other organizations such as WashPirg, Amnesty International, United Students Against Sweatshops, and La Raza Commission. Additionally, he became active in advocating for worker rights, particularly of undocumented workers; an issue that in late 2005 became even more important as Congress debated a harshly restrictive measure H.R. 4437. The proposed law would have penalized undocumented immigrants and made it a felony for anyone to provide aid to these individuals.
Across the country massive protests were organized to fight H.R. 4437, in 2006. In Seattle, Rosales worked with El Comite Pro-Reforma Migratoria y Justicia Social which organized a march on April 10, 2006, as part of the National Day of Action for Immigrant Justice. Furthermore, Rosales along with fellow UW MEChistA's organized a rally on campus that included student and faculty speakers. Rosales was also part of the May 1st Action Coalition that organized Seattle's May 1 rally, an event that drew an approximately 65,000 people.
Oscar Rosales Castaneda was interviewed by Josue Q. Estrada at the University of Washington on July 15, 2014.