This systematic review evaluated the measurement properties of the De Jong Gierveld Loneliness Scale (DJGLS) in adults. A systematic search of four electronic databases (PubMed, EMBASE, Scopus, and PsycINFO) was conducted from inception until December 2022. The COSMIN (Consensus-Based Standards for the Selection of Health Measurement Instruments) guidelines were used to assess the methodological quality and evidence synthesis of the included studies. Forty-six studies assessed the validity and reliability of the DJGLS-11 and its short version, the DJGLS-6. Very-low-quality evidence supported the content validity, moderate to high-quality evidence confirmed the structural validity and internal consistency, and low-quality evidence supported the construct validity of the two versions. Test-retest reliability was examined for the DJGLS-6 with low-quality evidence supporting excellent interclass coefficient values of 0.73–1.00. Both scales were cross-culturally adapted and translated into 18 languages across 12 countries. Although the structural validity and internal consistency of the DJGLS were supported by high-quality evidence, very-low to low-quality evidence was available for its other measurement properties. Future studies are needed to perform a more comprehensive assessment of the measurement properties of the DJGLS before fully recommending the scale to assess loneliness in adults.