The mesoporous dominant cashewnut sheath derived bio carbon is reported for the first time as anode material for lithium and sodium ion batteries (LIBs and SIBs). Primarily, cashewnut sheath carbon (CNSC) is synthesized through carbonization of cashewnut sheath, followed by KOH activation at temperatures such as 750, 800, 850 and 900 °C. Bestowed with a high surface area of 1967 m2 g−1, mesoporous dominant, porous sheet like structure with a pore radius of 2–8 nm and an acceptable electronic conductivity of 0.1638 mS cm−1, CNSC carbon activated at 800 °C offers ample scope to explore it further as probable anode material for LIBs and SIBs. CNSC-800 anode delivers a discharge capacity of 620 mAh g−1 at 100 mA g−1 for 100 cycles, 348 mAh g−1 at 200 mA g−1 for 100 cycles and 271 mAh g−1 at 500 mA g−1 upto 200 cycles in LIBs. Similarly, a progressive capacity of about 200 mAh g−1 at 100 mA g−1 for more than 100 cycles has been observed in SIBs. The in-house prepared CNSC-800 anode, when explored for high rate application demonstrates 55 mAh g−1capacity at 5 A g−1 condition for 300 cycles in SIBs, which is noteworthy.