Developing novel sorbents with maximum carbonation efficiency and good cycling stability for CO2 capture is a promising route to sequester anthropogenic CO2. In this work, we have employed a green synthesis method to synthesize CaO-based sorbents suitably stabilized by MgO and supported by in situ generated carbon under inert atmosphere. The varied amounts (10-30 wt %) of MgO were used to stabilize the CaO. The supported mixed metal oxide (MMO) sorbents were screened for high-temperature CO2 capture under CO2 rich (86% CO2) and lean (14% CO2) gas streams at 650 °C and atmospheric pressure. The MMO sorbents captured 53-63 wt % of CO2 per gram of sorbent under 86 and 14% CO2, accounting for about 98% carbonation efficiency, which outperforms the CO2 capture capacity of limestone derived CaO (L-CaO) sorbents (22.8 wt %). All of the synthetic MMO sorbents showed greater capture capacity and cyclic stability when compared to benchmark L-CaO. Because of the high carbonation efficiency and cycling stability of g-Ca0.69Mg0.3O sorbent, it was tested for 100 carbonation/regeneration cycles of 5 min each under CO2 lean conditions. The g-Ca0.69Mg0.3O sorbent showed exceptional CO2 capture capacity and cycling stability and retained about 65% of its initial capture capacity after 100 cycles.