The increasing cost and limited availability of lithium have prompted the development of high-performance sodium-ion batteries (SIBs) as a potential alternative to lithium-ion batteries. However, it has been a critical challenge to develop high-performance anode materials capable of storing and transporting Na⁺ efficiently. Amongst the various options, MoS₂ has significant advantages including low cost, and a high theoretical capacity of ∼670 mA h g⁻¹. Nevertheless, MoS₂ has several issues: its electronic conductivity is low and its structure deteriorates rapidly during charge/discharge cycles, leading to a poor electrochemical performance. Here, a dual-phase MoS₂ (DP-MoS₂) is synthesized by combining two distinct 1T (trigonal) and 2H (hexagonal) phases to solve these challenges. Compared to the conventional 2H-MoS₂ counterpart, the DP-MoS₂ phase material presents a highly reversible Na⁺ intercalation/extraction process aided by expanded interlayer spacing along with much higher electronic conductivity and Na ion affinity. Consequently, the DP-MoS₂ electrode delivers a high cyclic stability with a reversible capacity of 300 mA h g⁻¹ after 200 cycles at 0.5 A g⁻¹ and an excellent rate capability of ∼220 mA h g⁻¹ at 2 A g⁻¹. The SIBs assembled with DP-MoS₂ and Na₃V₂(PO₄)₃ as the negative and positive electrodes, respectively, have a specific capacity of 210 mA h g⁻¹ (based on the mass of DP-MoS₂) at 0.5 A g⁻¹. This performance demonstrates that DP-MoS₂ has a significant potential in commercial devices. This work offers a new approach to develop metal chalcogenides for electrochemical energy storage applications.