A plethora of literature exists on irrigation-induced agricultural development (IIAD). However, these studies deal only with the theoretical arguments and to date no proper investigation has been conducted to examine the distribution of the long-term benefits of IIAD in a semi-subsistence economy. This study investigates the long-term benefit changes of IIAD using data from the rice farming sector in Sri Lanka. The results show that: (1) IIAD has increased the overall social welfare through consumption of a larger quantity at a lower price, (2) non-farm sector gains are larger than the farm sector gains, (3) the distribution of the benefits among different types of producers depend on the magnitude of the expansion of the irrigated areas as well as the competition faced by traditional farmers and (4) selective technological adoption and subsidies have a detrimental effect on the welfare of other producers who do not enjoy the same benefits.