An analytical and numerical investigation of the performance of a dual-mode propulsion system using ionic liquids is presented. Chemical bi-propellant performance of select propellants is determined using Chemical Equilibrium with Applications. Comparison of predicted specific impulse of ionic liquids with hydrazine and UDMH show that the ionic liquid propellants have 3-12% lower specific impulse when paired with nitrogen tetroxide. However, when paired with hydroxlammonium nitrate, the specific impulse is comparable. Density Impulse for ionic liquids is found to be superior due to their higher density. Analytical investigation of an electrospray electric propulsion system shows that some ionic liquids are capable of operating in a purely ionic regime, providing very high specific impulse (∼ 6000 sec). The predicted chemical and electric performance data will be used to quantify mass savings for representative dual-mode propulsion missions.