We have investigated the non-standard interaction mediated by a scalar field at the upcoming long-baseline neutrino experiments, Protvino to Super-ORCA (P2SO) and Deep Underground Neutrino Experiment (DUNE). Specifically, we have studied the sensitivity of these two experiments to constrain the diagonal Scalar Non-standard interaction (SNSI) parameters \(\eta _{ee}\) , \(\eta _{\mu \mu }\) and \(\eta _{\tau \tau }\) and how the measurements of mass hierarchy, octant of \(\theta _{23}\) and CP violation (CPV) sensitivity is affected in the presence of SNSI. Our key finding is that \(\Delta m^\textrm{2}_{31}\) has a very non-trivial behavior in the presence of \(\eta _{\mu \mu }\) and \(\eta _{\tau \tau }\) when we consider SNSI does not exist in nature. Both the experiments are very sensitive to these SNSI parameters, but for \(\eta _{ee}\) , DUNE provides a stringent bound compared to P2SO. Mass hierarchy and CPV sensitivity are affected mainly by \(\eta _{ee}\) compared to the other two parameters. In contrast, octant sensitivity is mainly affected by \(\eta _{\mu \mu }\) and \(\eta _{\tau \tau }\) if we consider SNSI to exist in nature. The sensitivity of the measurements is either higher or lower than that of the standard case, depending on the relative sign of these parameters.