•Mg2Si powder directly produced by liquid–solid reaction method.•Resulting powders were identified as single phase Mg2Si by XRD and EDX analysis.•After 973 K heat treatment for 10 h, all the Si powders produced Mg2Si powders.•Mg2Si particles were larger (75–106 μm) than starting Si particles (53–75 μm).•Mg2Si powder yields reached at least 90%.The synthesis and powder processing of compounds in an Mg2Si system are difficult to achieve. These processes require a multi-step procedure that involves melting, crushing, grinding, and sieving in order to obtain Mg2Si powders from the Mg and Si starting materials. This may lead to the oxidation of Mg and contamination of the obtained powders with impurities. In this study, we developed a direct technique for synthesizing Mg2Si particles using a liquid–solid reaction. Si powders of various particle sizes (20–38, 38–53, 53–75, 75–106, 106–150, and 150–250 μm) were employed in the synthesis. The resulting powders were identified as single phase of Mg2Si by both XRD and EDX analyses. The optimal heat treatment temperature was between the two eutectic temperatures, 911 K and 1218 K. After heat treatment at 1143 K for 4 h, Si powders with particle sizes of less than 53 μm did not yield Mg2Si powders. In contrast, after heat treatment at 973 K for 10 h, all the Si powders produced Mg2Si powders. The Mg2Si powder particles were larger than the starting Si particles; for example Si particles with sizes of 53–75 μm produced Mg2Si powders with sizes ranging from 75 to 106 μm. The yields of Mg2Si powder reached approximately 90%.