The pion–argon cross-section measurement is crucial to understanding effects such as final state interactions, which account for a large source of systematic uncertainty in neutrino oscillation experiments. ProtoDUNE-SP, with its beam of charged particles, can provide such experimental constraints. This paper elaborates on the methodology to measure the cross-section on large-scale liquid argon time projection chambers like ProtoDUNE-SP. We use the 1 GeV Monte-Carlo (MC) sample to demonstrate the analysis procedures. The cross-section measurements for pion kinetic energy ranging from 350 MeV to 950 MeV are performed on the MC sample. The consistency of the MC results with its input values serves as validation of the method and the procedures, which we will later use to perform measurements on the data sample.