[1] His uncle Franz Leuninger was a Christian trade unionist active in the German resistance to Nazism, who was executed on 1 March 1945 at the Plötzensee Prison.

[1][2] After his Abitur at the Gymnasium Philippinum Weilburg [de], Leuninger studied philosophy and theology.

Leuninger served as a member of the board of the European Council on Refugees and Exiles based in London.

[4] In 1986, he founded with Jürgen Micksch and others in Frankfurt Pro Asyl, a human rights organisation for refugees seeking asylum in Germany.

[2][1] Besides dealing with questions of the Church and theology, Leuninger was involved with topics related to asylum in Germany, such as Integration von Zugewanderten [de] (integration of immigrants), Fremdenfeindlichkeit (Xenophobia, literally: hostility towards strangers], and Multikulturelle Gesellschaft [de] (multi-cultural society) and published on these areas.