The Belt and Road Initiative (BRI) which was executed in 2013 has seen tremendous growth in investment and trade among participating countries; however, participating countries are reeling from high levels of non-performing loans and high execution risks. This motivates the present study to empirically quantify the impact of financial development on the economic growth of 41 BRI countries from 2000 to 2018. The study also explored the threshold beyond which financial development will be beneficial or detrimental to the economic growth in the BRI countries. Finally, this study assessed the causality relationships between financial development and economic growth among BRI countries. Using the instrumental variable generalized method of moment model for the empirical analysis, and the panel threshold model for the threshold analysis, the findings showed that financial development spurs BRI countries’ economic growth. This result was robust by separating the sample into different income groups. Also, the panel threshold results showed that financial development spurs BRI countries’ economic growth at both the lower and upper threshold regimes of financial development; however, the lower threshold regime has a higher economic growth effect of financial development. Thus, less finance is beneficial to BRI countries’ economic growth. Finally, the study found a bi-directional causality between financial development and economic growth among BRI countries. The study proposes promoting a stable financial system among BRI countries by reducing non-performing loans and ensuring sustainable and efficient utilization of financial resources.