in august 2006 mertes was appointed state secretary for federal, european and international affairs in the state government of north rhine-westphalia (düsseldorf). in that capacity, he was plenipotentiary of north rhine-westphalia to the federation (berlin) and the state’s representative to the european union (brussels). he left office in 2010 after the change of government from a cdu-led to an spd-led state government. in 2011 he became head of the konrad adenauer foundation’s jerusalem office.