The hydroxyl radical (radical dotOH) is omnipresent and indispensable in environments from Earth’s atmosphere to biological system. Plasma-facing liquids (PFLs, e.g., raindrops in the vicinity of lightning and laboratory-scale plasma applications) have attracted attention because they facilitate storage of reactive oxygen and nitrogen species (RONS), including radical dotOH, produced by plasma. As the hydroxyl radical is considered as one of the most powerful oxidants and the most important intermediate of chemical processes in PFLs, it has become increasingly significant; however, some of radical dotOH generation mechanisms, particularly photo-induced productions, remain ambiguous. In this contribution, we show that N(III) [i.e., nitrite anion (NO2−) and nitrous acid (HONO)] and hydrogen peroxide (H2O2) have not been significantly considered as sources of radical dotOH in PFLs. The contribution of N(III) and H2O2 photolysis to radical dotOH production is estimated by numerical and experimental approaches. The results of the model experiments show that the concentration of radical dotOH generated by UV photolysis of N(III) due to plasma emission is approximately 20% of the total concentration in a PFL. Thus, the unique feature of a plasma jet results in self-enhancing and self-focusing radical dotOH production in PFLs. Furthermore, we demonstrate that additional light exposure is the effective way to enhance radical dotOH production in a PFL.