Linear transformer driver (LTD) technology allows a pulsed-power generator to be transportable due to its salient features in compactness and modular design. To further reduce the footprint of an MA-class pulsed-power generator, nested transmission lines were designed and tested for current adding in a four-stage gas-insulated LTD module. The current adder assembly contained two modules that were charged in opposite polarities. Each module held two LTD cavities that shared a common electrode of the nested transmission line with deionized water insulation. Post-hole convolutes were installed for the aggregation of the output current of different modules. More specifically, numerical simulations were conducted to calculate the nested line inductance, which revealed that the total system inductance was ∼10 nH in the nested geometry. Experimentally, testing on the four-stage LTD prototype showed that the LTD module can deliver a 1.2 MA current peak with a rise time of 140 ns to a short circuit load under the charging voltage of ±50 kV, which validated the applicability of using nested lines for current adding in an MA-class LTD module.