From 1973 to 1998, he was a professor of Modern History at the Bundeswehr University Munich.
As a child, Seidler came as a refugee to West Germany, following the expulsion of Germans after World War II by the Czechoslovak government from his native Moravian Silesia.
From 1959 to 1963 he was Deputy Director of the Bundeswehrfachschule in Cologne, and was subsequently employed by the Federal Ministry of Defence, as an Adviser in the Department of Administration and Law, from 1963 to 1968.
He was Scientific Director of the Heeresoffiziersschule München from 1968 to 1972, and attended the NATO Defence College Senior Course in Rome in 1972.
[4] A reviewer in the conservative Frankfurter Allgemeine Zeitung, writing about Seidler's book Phantom der Berge, stated: "Since his retirement he publishes one book after the other, with which he has distanced himself from serious historical research.