Iran’s construction industry operates in an economic environment characterized by price volatility, inflation, exchange-rate instability, and financial uncertainty. Under such conditions, insufficient contractual flexibility may intensify disputes, cause project delays, and adversely affect construction quality. This study investigates the role of flexibility in three-party construction contracts in achieving project success under Iran’s unstable economic conditions. A qualitative research approach was adopted within an interpretivist paradigm. Data were collected through semi-structured interviews with 12 industry experts, including contractors, consultants, and employer representatives, who were selected using purposive sampling. The data were analyzed using thematic analysis based on Braun and Clarke’s six-phase framework. The novelty of this study lies in identifying and explaining the key components of flexibility in three-party construction contracts under conditions of economic instability in Iran, while simultaneously considering the interests of all major project stakeholders. The findings indicate that the financial system and adjustment mechanisms constitute the most critical components of contractual flexibility. Key strategies identified include the use of reliable adjustment indices, adjustment calculations based on inflation rates, the possibility of applying exchange-rate adjustments under specific circumstances, revising the basis for cost estimation and payment, and compensating for fluctuations in material prices. Contractual flexibility contributes to construction project success by mitigating economic risks, controlling costs, preventing project suspension, maintaining construction quality, and strengthening cooperation among contracting parties. It can therefore help mitigate some of the adverse effects of an unstable economic environment. The findings provide a practical basis for employers, consultants, and contractors to reconsider and improve the financial and price-adjustment provisions of three-party construction contracts, thereby reducing contractual disputes and implementation-related conflicts.