The increasing complexity of European air traffic, together with persistent capacity shortages in Air Traffic Service Units (hereinafter ATSUs) created the need for innovative approaches to optimise Air Traffic Controller (hereinafter ATCO) allocation and sector management. In this context, the SESAR project IFAV3 (Increased Flexibility of ATCO Validation) was initiated, encompassing four complementary strategies. This paper focuses on the validation of the Smart Sector Grouping (SSG) strategy, which is divided into two complementing use cases. The first addresses ATCO rostering process aiming to improve the flexibility and efficiency of controller allocation. The second introduces the SSG process-tool, designed to support Airspace Managers (hereinafter ASMs) in defining optimal sector groups within an ATSU improving the current method, thereby maximising the potential of the IFAV concept. Two validation exercises were conducted, one in Sweden and one in Spain, to assess the feasibility, operational benefits, and impact of the strategy. Results of both use cases suggest that Smart Sector Grouping can reduce workload, improve decision-making, and enhance the efficient use of ATCO qualifications without compromising safety. The research presented in this paper has been conducted in the frame of the European IFAV3 project. The IFAV3 project has received funding from the SESAR 3 Joint Undertaking under grant agreement No 101114683 under European Union’s Horizon Europe research and innovation programme.