The reforming of hydrocarbons has gained much interest as a means to upgrade low-grade fuels and to produce value-added chemicals. Plasmas have been considered one of the potential ways to reform fuels to achieve more effective and cleaner combustion, particularly by producing various hydrocarbons, hydrogen carriers, and oxygenates as well as syngas. Here, we employed a submerged microwave plasma jet of argon to investigate its potential to transform n-heptane. We found that the product selectivities were mainly governed by the effective gas temperature, which we adjusted by changing the energy density of the argon stream. The transformation of n-heptane by this method mostly produced ethylene and acetylene, which is different than the products produced by pyrolysis or a chemical equilibrium composition. Such unique selectivities could be attributed to the rapid quenching of the microwave plasma jet upon direct contact with the colder liquid. The transformation of n-heptane was significantly affected by the interactions between the microwave plasma jet and the liquid n-heptane. To support our results, we include a detailed chemical analysis and discussion of the physical characterization of the microwave plasma jet using optical emission spectroscopy.