Nanoscale materials have been explored as better alternatives to conventional therapeutic agents in cancer theranostics in the recent period due to efficacy in overcoming biological, biomedical, and biophysical barriers. Analysis on the ability of copper nanocluster (CuNC)-doped hydroxyapatite nanoparticles (Cu-HXNPs) as suitable nanocarriers for anticell proliferative application was carried out. Having high adsorption capacity, the Cu-HXNPs could be loaded with the anticancer drug quercetin, which is a polyphenolic flavonoid compound, and were used as nanocarriers to be applied on HeLa (cancer cells) and HEK-293 (normal cells). The drug release profile was found to be pH-dependent, where maximum release of quercetin from quercetin-loaded Cu-HXNPs was observed in acidic pH as compared to physiological pH. The Cu-HXNPs could release quercetin, which could effectively decline proliferation of cancer cells via generation of reactive oxygen species. Moreover, the released quercetin significantly altered the cell cycle pattern and triggered the cells to undergo apoptosis. Additionally, the efficacy of Cu-HXNPs as a nanocarrier to release quercetin on 3D spheroids of HeLa had been checked, which demonstrated significant reduction in the viability of 3D spheroids. The luminescent CuNCs used for doping HXNPs endowed the nanocarrier with the imaging property, which was an excellent feature in confirming their uptake by the cells. Thus, the study suggested Cu-HXNPs to be a beneficial nanocarrier for both bioimaging and therapeutic purpose in the field of cancer theranostics.