Van Osch joined the Royal Netherlands Military Academy in 1974 and was commissioned as an artillery Officer in 1978.

Van Osch attended the United States Army Command and General Staff College, followed by a tour as a Lieutenant Colonel and lecturer in strategy at the Netherlands Defence College, during which time he also studied at Leiden University for a master's degree in Public Administration.

Subsequently, he was appointed as Head of Policy Development for the Directorate of Personnel and Organization of the Royal Netherlands Army.

In June 2002 Van Osch was promoted Brigadier General and took over the post of Director of Operations in the Dutch Ministry of Defence.

[1] In June 2007, Lt Gen van Osch was appointed as the Military Representative of The Netherlands to the EU and NATO in Brussels.