The endemic Algerian myrtle, Myrtus nivelii Batt & Trab., was evaluated for its bioactive properties, such as antioxidant, anti-inflammatory, cytotoxic and antibacterial activities, and correlated with the individual phenolic compounds identified in its crude aqueous extract and subsequent organic fractions (ethyl acetate and butanol). Flavonols, such as myricetin, kaempferol and quercetin glycoside derivatives, were the major phenolic compounds found, along with the presence of ellagitannins. The ethyl acetate fraction contained the highest amount of phenolic compounds, followed by the butanol fraction and, finally, the crude aqueous extract. In general, all samples exhibited an excellent bioactivity, namely the ethyl acetate fraction that presented strong antioxidant activity, when compared to the standard trolox, strong cytotoxicity and antibacterial activity, especially against MRSA and MSSA. The present study revealed that the ethyl acetate fraction of M. nivelii could be used as a source of bioactive compounds in the food and pharmaceutical industries.