in 1981 mertes worked for carl otto lenz mp as a parliamentary assistant. from 1984 to 1987, he held various positions in the federal administration (federal ministry of defense, federal chancellery, federal ministry for the environment, nature conservation and nuclear safety). in 1987 chancellor kohl appointed him as his chief speechwriter. after the fall of the berlin wall mertes co-authored the „ten point program for german and european unity” which kohl presented on november 28, 1989. in 1993 he became director, policy planning, and in 1995 he was appointed director-general, policy planning and cultural affairs at the federal chancellery.