Modern diesel engines are seeing increasing system and after-treatment complexity which can lead to significant increases in the exhaust back pressure (EBP). This increases the amount of trapped residuals, raising the charge temperature but reducing the oxygen concentration. In this work, these effects of the EBP on diesel engine performance and emissions under conventional and low-temperature diesel combustion (LTC) regimes were investigated. Increasing the EBP resulted in higher pumping work for both combustion modes. While for conventional diesel combustion the effect of the EBP on combustion and emissions were not significant, for LTC the higher back pressures influenced the combustion and emissions formation processes. At low-load conditions, the increase in the charge temperature advanced combustion; at intermediate-load conditions, the reduction in the oxygen concentration delayed it. Smoke emissions were significantly reduced by a higher back pressure at intermediate-load conditions.