The construction of a national unified market is a crucial force in reducing regional development disparities. Based on the data from 31 provinces in China from 1993 to 2022, the impact of the national unified market on regional development disparities is examined. Furthermore, the mediating role of factor mobility and the moderating effect of informatization level are explored. The findings indicate that the construction of the national unified market exhibits a significant inverted U-shaped effect on regional development disparities. Labor mobility, capital mobility, and technology mobility are the key pathways through which the unified market influences regional development disparities. Additionally, informatization level positively moderates the inverted U-shaped relationship, advancing the turning point where disparities begin to decline. However, low geographic accessibility and high resource dependence may constrain the regional equalization effects of the national unified market.