Engine transient operation has attracted a lot of attention from researchers due to its high frequency of occurrence during daily vehicle operation. More emissions are expected compared to steady state operating conditions as a result of the turbo-lag problem. Ambient temperature has significant influences on engine transients especially at engine start. The effects of ambient temperature on engine-out emissions under the New European Driving Cycle (NEDC) are investigated in this study. The transient engine scenarios were carried out on a modern 3.0 L, V6 turbocharged common rail diesel engine fuelled with winter diesel in a cold cell within the different ambient temperature ranging between +20 °C and −7 °C. The engine with fuel, coolant, combustion air and lubricating oil were soaked and maintained at the desired test temperatures during the transient scenarios. Instantaneous engine performances including torque and speed, gaseous emissions such as CO, THC and NOx, and particulate emissions for its number and mass are analyzed during each transient scenario under different ambient conditions. Total cumulative gaseous and particulate emissions during the NEDC are examined quantitatively along with the engine parameters for each ambient temperature. The results show that almost all of the engine emissions increase with the decreasing ambient temperature, the highest specific gaseous and particulate emission is at the earlier stage of the NEDC.