•Development of a dual-functional intervention method for reinforced concrete beams.•Experimental programme on simply supported beams repaired by ICCP-SS method.•Analysis on the structural responses of simply supported beams with C-FRCM strengthening.•Comparison of test results with existing design methods.•Recommendation of changes on the design methods for cross-section capacity prediction. Chloride ions in marine environment can cause corrosion of steel reinforcement in reinforced concrete (RC) structures and result in structure deterioration. This study investigates a dual-functional intervention method, i.e. impressed current cathodic protection – structural strengthening (ICCP-SS) method, using carbon fibre reinforced polymer (CFRP) as both the anode material for impressed current cathodic protection and strengthening material for structural strengthening system. The effectiveness of the ICCP-SS method on the improvement of durability of RC structures is considered in a long-term timeframe. An experimental programme comprising nine simply supported beams is presented in this paper. The beams experienced 360-day accelerated corrosion and 180-day cathodic protection, followed by four-point bending tests. Flexural behaviour and capacities of the degraded beams repaired by using ICCP technology, structural strengthening technology and ICCP-SS technology were obtained. After the tests, the steel reinforcement bars inside concrete were taken out and cleaned to measure the section reduction due to corrosion. Results showed that the ICCP-SS technology can prevent the corrosion of the steel reinforcement effectively and increase the capacities of the beams at the same time. Finally, the appropriateness of existing design approaches for the intervened beams was also discussed in the paper. The ICCP-SS intervention method is found to be beneficial for the durability of RC structures in marine environment.