After attending studies in electrical engineering at Bundeswehr University of Munich, he became commanding officer of Light Infantry Battalion 112 in 1977, stationed in Regen, Bavaria.

Returning to Germany, he served with Armoured Brigade 6, stationed in Hofgeismar, Hesse, in 1989, before being appointed Chief of Staff for 4 Panzergrenadier Division, based in Erfurt, Thuringia.

[1] Between October 1999 and May 2003, Rossmanith held a variety of staff posts, after which he took command of 9 Armoured Brigade, based in Münster, and deployed for a second tour in the Balkans, commanding Multinational Brigade Southwest, part of the Kosovo Force.

He held the command until 2005, when he was appointed Deputy Director, Policy Planning and Advisory Staff at the Ministry of Defence, after which he became Chairman for Deployable Forces Coordination Group at Supreme Headquarters Allied Powers Europe (SHAPE) until 2009.

[1] He took command of the stability division of the International Security Assistance Force (ISAF), succeeding Maj. Gen. (ITA Army) Claudio Mora, in October 2010.