PurposeThis study aims to examine the relationship between financial inclusion and financial system development in emerging and frontier markets.Design/methodology/approachUsing data across 35 countries over 19 years (2004–2022), the improved GMM estimation technique reveals that financial inclusion significantly contributes to the development of financial systems.FindingsThe study uses a segmented approach, dividing financial development indices into subindices: financial depth, financial access and financial efficiency. Indicators of bank financial inclusion show a positive and highly significant relationship with bank depth and access but a negative relationship with bank efficiency. Similarly, indicators of the debt market and stock market financial inclusion demonstrate positive relationships with market depth and access but negative relationships with debt and stock market efficiency. The study further examines composite indexes of financial inclusion for bank, debt and stock market segments, finding strong and highly significant relationships with market development. These results underscore the importance of promoting financial inclusion across all segments of the financial sector to achieve an inclusive financial system.Practical implicationsThe implications of this research highlight the need for policymakers and practitioners to implement policies and regulations that enhance financial inclusion and foster the development of robust financial systems. By extending access to mainstream financial instruments and services, financial institutions can stimulate financial intermediation and support, thereby accelerating the development of the banking, debt and stock markets.Originality/valueThe study is robust to the use of several indicators of financial inclusion and financial development, and it forms part of the early studies that examine the close relationship between the two variables.