Of the many fullerene derivatives that have been examined, cationic functionalization has proven to be most promising for aqueous or biological applications. Until recently, however, no cationic colloidal fullerene aggregates in the nanosize regime have been characterized in the aqueous phase. The results presented here represent the most rapid and efficient, to the best of our knowledge, viral inactivation reported for any colloidal fullerene aggregates. Tris-adducted fulleropyrrolidinium aggregates are prepared and analyzed for concentration-dependent singlet oxygen (1O2) production and MS2 bacteriophage inactivation. Experiments are performed under visible, UVA, and sunlight irradiation with the addition of natural organic matter (NOM) to simulate environmental conditions. Viral inactivation was observed at sensitizer concentrations in the nanomolar range. A 5-log inactivation of MS2 was observed after 4 or 1 min of sunlight exposure with 250 nM fullerenes with or without NOM, respectively. The environmental implications of these results are discussed in the context of previously reported 1O2-mediated MS2 inactivation.