Dissimilar metal welded joints (DMWJs) are essential components in offshore oil and gas infrastructure, yet they face critical degradation through corrosion-fatigue interaction under sour service conditions. This comprehensive review examines the multi-physics mechanisms governing crack initiation and propagation in DMWJs exposed to sour environments containing H₂S, where fatigue lives can be reduced by factors of 10× to 50× compared to air . The electrochemical and mechanical coupling arises from hydrogen embrittlement, where hydrogen generated at the crack tip diffuses into the fracture process zone (FPZ) and degrades material cohesion . Microstructural heterogeneity across the weld—including the heat-affected zone (HAZ), fusion boundary, and buttering layers—creates complex local stress-strain fields and galvanic corrosion cells that accelerate damage . Welding residual strain and ductility dip cracking have been identified as critical promoters of corrosion fatigue crack initiation in DMWJs, with cracks initiating preferentially at weld interfaces or regions of high residual strain . Advanced predictive models based on hydrogen transport kinetics to the FPZ have been developed to quantify corrosion fatigue crack growth (CFCG) rates over wide ranges of mechanical variables (ΔK, stress ratio, frequency) and environmental variables (H₂S partial pressure, pH, temperature) . The transition from short-crack to long-crack behavior in sour environments reveals that shallow flaws can grow up to an order of magnitude faster than deep flaws at equivalent ΔK, highlighting the non-conservatism of deep-crack data for shallow flaw assessment . This review concludes that effective life prediction requires integrated multi-physics frameworks coupling crack-tip electrochemistry, hydrogen diffusion, and fracture mechanics.