Apacite (apatite-calcite) nanocomposites have been synthesized using an environmentally friendly, affordable, and one-step method relying on deep eutectic Calcoline (calcium chloride-choline chloride). The deep eutectic system plays as an all-in-one system providing all requirements for the one-step synthesis of Apacite nanocomposites including reactants, reaction medium, particle growth controller, and platform for carbon (atmospheric CO2) capture and conversion into calcite. The characterization results confirm the synthesis of nano-particulate Apacite composites composed of apatite crystallites with an average size of 25 nm and calcite crystallites with a mean size of 35 nm in the phase ratio 53 wt% apatite: 47 wt% calcite. The biological results obtained on in vitro bioactivity and behavior of hMSCs emphasize on favored non-toxicity, bioactivity, and osteogenic properties of as-synthesized Apacite nanocomposites. It seems that the nanoscale structure, high aspect ratio, low crystallinity, improved dissolution and ion release of Apacite nanocomposites provide the optimum conditions for cellular growth and differentiation without signs of toxicity.