Na-ion batteries (SIBs), perceived as the most promising alternative energy storage technology, are attractive for large-scale stationary applications due to the cost effectiveness and global abundance of sodium. One of the formidable challenges in the way of their extensive commercialization is the development of suitable low-cost positive electrode materials with high energy density and long cycle life. In this study, a phosphite-based layered polyanionic material with the formula, Na2[(VOHPO3)2(C2O4)]·2H2O, has been investigated as a novel positive electrode for SIBs. The material was synthesized through a room temperature precipitation method and undergoes reversible Na+-ion insertion at an average discharge voltage of 3.65 V which is higher than that of the same V4+/V5+redox couple of NaVOPO4(3.4 V) in a non-aqueous Na cell. The material exhibits a high discharge capacity of ∼101 mA h g−1at 0.1C rate in Na half-cells. Capacity fading encountered by the pristine material was overcome with the help of ball-milling with carbon. The layered material facilitates the migration of large Na+ions, resulting in a superior rate performance (∼80 mA h g−1at 10C rate). In addition, a long-term cycling stability over 1000 cycles was demonstrated at 2C rate with 62% capacity retention.OperandoXRD studies reveal that the reversible Na+-ion insertion in the framework happensviaa bi-phasic mechanism. The feasibility of full cells was demonstrated using NaTi2(PO4)3as the negative electrode and the full cell exhibited a reversible capacity of 71 mA h g−1at 0.1C rate and 65 mA h g−1at 1C rate with good capacity retention.