In the national strategy of promoting high-quality development, fostering corporate new quality productive forces, with technological innovation at its core, is of particular importance to the manufacturing sector. Using data from Chinese A-share listed manufacturing firms from 2015 to 2023, this study examines the impact of audit committee diligence on new quality productive forces and explores the underlying mechanisms. The empirical results show that audit committee diligence has a significant inverted U-shaped relationship with new quality productive forces: a moderate increase in diligence helps enhance new quality productive forces, whereas excessive diligence exerts a suppressing effect. Mechanism tests indicate that an appropriate level of diligence promotes new quality productive forces by improving internal control quality; however, when diligence becomes excessive, the decline in firms’ risk-taking weakens or even reverses this positive effect. The moderating effect analysis further reveals that audit committee independence flattens the inverted U-shaped relationship. These findings provide policy and practical implications for the operational arrangement of audit committees and the improvement of internal control systems.