Application of atmospheric-pressure spark discharge plasma for conversion of the two most important anthropogenic greenhouse gases (GHGs) into valuable products, including syngas and multiwalled carbon nanotubes (MWCNTs), is experimentally evaluated. Syngas with different CO/H2 ratios and MWCNTs with different physicochemical properties can be generated by varying the CO2/CH4 feeding ratio from 0 to 3. Operating spark discharge with pure CH4, the reactor generates syngas with the lowest rate and MWCNT without oxygen-containing functional groups. Introducing an appropriate amount of CO2 into plasma results in higher syngas and MWCNT generation rates. To achieve the highest syngas generation rate, a CO2/CH4 ratio of 1 is suggested, while for the highest MWCNTs generation, a CO2/CH4 ratio of 1/3 is favored. Moreover, the physicochemical properties of the MWCNTs generated are influenced via controlling the CO2/CH4 ratio, and various characteristic properties of MWCNTs may provide different applications. Overall, simultaneous generation of MWCNTs and syngas as demonstrated in this work can be a promising technique for carbon capture, utilization, and storage (CCUS).