Direct proof of use
Rheinmetall's service-history account says the first Marder 1A5A1 vehicles reached the German contingent in Afghanistan at the end of 2007. It places up to 35 Marder IFVs at Mazar-e Sharif and, from 2009, Kunduz to reinforce the Quick Reaction Force.
Bundeswehr material on the 2 April 2010 Good Friday battle states that the Schuetzenpanzer Marder was in Afghanistan for camp security and support to combat troops, including the Quick Reaction Force, and that it was first used in combat in 2009.
Sources: Marder infantry fighting vehicle - The Marder turned 50 in 2021, 2 April 2010: The Good Friday Battle
Timeline
The documented Afghanistan record starts with the 1A5A1 deployment at the end of 2007 and then shifts toward heavier use in northern Afghanistan from 2009. Rheinmetall identifies Mazar-e Sharif and Kunduz as the main areas for the deployed Marder contingent.
By 2010, ZMSBw describes the German Quick Reaction Force and the successor training-and-protection battalions as equipped with Marder IFVs, Panzerhaubitze 2000 howitzers, and mechanized engineer vehicles during intensified operations around Kunduz.
Sources: Marder infantry fighting vehicle - The Marder turned 50 in 2021, ZMSBw Military Operations in Afghanistan
Narrative
The Marder appeared in Afghanistan as part of Germany's ISAF contribution rather than as an Afghan-government vehicle. Its role was tied to protected movement, camp security, convoy and patrol escort, armored reserve duties, and fire support for German combat formations in the north.
Rheinmetall describes the Marder as often operating in mixed formations with wheeled protected vehicles such as the Dingo. The same account says northern Afghanistan's open and broken terrain suited the tracked IFV, while large IEDs, concentrated RPG fire, and heat in the fighting compartment were major operational problems.
Bundeswehr's withdrawal overview separately characterizes the Marder as part of the Quick Reaction Force and the training-and-protection battalions because of its armor protection and firepower. ZMSBw notes that these formations used the vehicles more as infantry tanks during the shift from stabilization tasks toward more intensive combat operations.
Sources: Marder infantry fighting vehicle - The Marder turned 50 in 2021, Bundeswehr Afghanistan Withdrawal Overview, ZMSBw Military Operations in Afghanistan