Owing to their unique properties, ionic liquids (ILs) have become a real alternative to organic compounds. Nowadays, ILs are commonly used in a number of areas such as chemical synthesis and separation techniques. However, ionic liquids continue to have a limited applicability in industry because the information on their physical and chemical properties is not readily available. This paper presents, for the first time, the results of studies on 1-hexyl-1,4-diaza[2.2.2]bicyclo octanium bis(trifluoromethylsulfonyl)imide ([HDABCO][NTf2]) ionic liquid which is relatively novel and not well researched. A wide range of properties, important from a point of view of potential applications of [HDABCO][NTf2], was examined. Parameters such as density, phase transition temperatures, long-term thermal stability, polarizability, hygroscopicity, and McReynolds constants have been determined.