The 1,10-phenanthrolinium cation and 3-hydroxy-2,4,6-trinitrophenolate anion are held together through an N—H⋯O hydrogen bond. In the crystal, cation–anion pairs are connected by C—H⋯O hydrogen bonds, forming a chain structure along [101]. Spectroscopic data also support the formation of a molecular salt. Sensitivity tests and thermal testing indicate that it is an insensitive high energy density material (IHEDM).