His mother's family roots lay in East Prussia and Brandenburg, which has subsequently underpinned both his interest in the history of those regions and his increasingly public genealogical research.
Kühn passed his school final exams (Abitur) in West Berlin in 1956 which opened the way to a university level education.
In the 1965 General Election the FDP won 9.5% of the national vote and prepared to rejoin the governing coalition as a junior partner.
The FDP group in the Bundestag (national parliament) identified a critical vacancy for a lawyer to work as a parliamentary research assistant and offered Kühn the job.
In a discussion the newly elected leader of the FDP group in the Bundestag, Hans-Dietrich Genscher, who would become an important political ally, urged him to accept.
Party colleagues were appreciative of the part he played in securing excellent national results in the elections of 1965 and 1969 and there was a widespread assumption that he would himself become a member of the Bundestag.
This faction did not share Detlef Kühn's supportive attitude to Erich Mende, by now seen a liberal leader from and for an earlier generation.
[1] Instead, with the support of Hans-Dietrich Genscher who had apparently by now become an indispensable member of the government, Detlef Kühn succeeded to the presidency of the Whole Germany Institute ("Bundesanstalt für gesamtdeutsche Aufgaben" / BfgA).
He succeeded Ludwig A. Rehlinger who was out of sympathy with the controversial Ostpolitik ("East [Germany] policy") being pursued by the Brandt government.
Kühn remained in the job, which defined his career, for a remarkable seventeen years, stepping down only after reunification made the BfgA politically redundant.
It quickly became apparent that this arrangement was opposed by Saxony's western born Minister-president Kurt Biedenkopf, who had very clear ideas of his own about an alternative broadcasting hub for Dresden.