<p>Application of weldment design guidelines to fatigue life estimation of welded joints in the literature has been mostly focused on single-channel loading conditions, while more effort should be made to address realistic loading scenarios such as multi-channel loading cases. part I of this two-part publication reviewed BS-7608, IIW, and EC3 design guidelines and applied them to fatigue life prediction of steel-welded tubular joints with partial weld penetration under CA and VA single-channel axial and torsional loadings. In this part II, the guidelines’ recommendations are applied to multi-channel fatigue life prediction of steel-welded joints. For out-of-phase CA multi-channel loading, the IIW guideline resulted in life estimations within a factor of 3 on the safe side, as compared to a factor of 5 with high conservative tendencies based on BS-7608 and EC3 guidelines. Three methods are outlined for analysis of multi-channel VA loading cases based on the modified Palmgren–Miner method, equivalent stress signal, and interaction equations. Based on the results, the modified interaction equation method achieved the highest accuracy (within a factor of 3) among the three methods for multi-channel VA loading conditions. The equivalent stress reformulations of the interaction equations showed good applicability to multi-channel CA and VA life estimations. In general, predictions by the IIW guideline were more accurate with better proportional and nonproportional data consolidation compared to EC3 and BS-7608.</p>