Within the joint public funded project “H2 ICE Democar”, funded by the Federal Ministry for Economic Affairs and Climate Action, Ford, Bosch, MAHLE, Umicore, Institute of Automotive Engineering (IFS, University of Stuttgart), Research Institute for Automotive Engineering and Powertrain Systems (FKFS), Chair of Thermodynamics of Mobile Energy Conversion Systems (tme), DHL, Purem by Eberspächer and Shell are identifying the key requirements for a hydrogen (H2) engine hybrid powertrain in a light commercial vehicle. This powertrain technology enables the CO2-free operation, long driving ranges, fast refueling and zero-impact exhaust emissions in combination with a high thermal efficiency of the H2 engine. This paper focuses on the optimization of the exhaust gas treatment (EGT) concept for the H2 engine serial hybrid powertrain. An efficient EGT system is the key to combine low tailpipe emissions with high engine thermal efficiency. Even though the lean combustion concept (λ > 2) provides already relatively low engine-out exhaust emissions, a dedicated H2 EGT system has been implemented to reduce the tailpipe emissions even further. Suitable catalyst technologies have been identified at a model gas test bench. In addition to the requirements of the lean H2 operation engine concept, the EGT optimization has to fulfill the demands of the vehicle package. During the project the preselected catalyst technologies have been verified by engine tests under stationary and transient conditions. This supports the holistic assessment and optimization of the EGT system in the “H2 ICE Democar” project. A further important aspect is the serial hybrid vehicle operating strategy that offers additional degrees of freedom to further reduce emission especially with respect to transient engine operation. The results demonstrate the potential of a lean-burn H2 engine combustion concept equipped with an appropriate EGT system. Tailpipe emissions have been minimized without compromising engine efficiency.