mertes has been a member of the cdu since 1971, the "kuratorium der freunde und förderer des leo baeck instituts e.v." since 1988, the international advisory council of the "moscow school of civic education" since 2000, the international board of directors of the "institute for human sciences at boston university" 2001-2009, the "commission for contemporary history" since 2002, and the drafting committee for the cdu’s new party platform (grundsatzprogramm) 2006-2007. in 2006 he received, together with rabbi nathan peter levinson and protestant pastor johannes hildebrandt, the international raoul wallenberg foundation's "roncalli award" for interfaith dialogue and understanding.