Refractory high-entropy alloys (RHEAs) are a promising new class of multi-principal component alloy systems that have attracted extensive interest from researchers owing to their impressive structural and mechanical properties at high temperatures. However, the real-world applications for RHEAs are restricted, due to the low strain hardening capability and resultant poor ductility at ambient temperatures. In comparison with the ‘3d transitional group’ face-centred cubic (FCC) HEAs, the low ductility and strain hardening exhibited by RHEAs is mainly attributed to the lack of closely-packed planes and relatively high critical resolved shear stress, which is necessary to activate the slip systems in the body-centred cubic (BCC) structure. Recent research has shown that twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects were successfully engineered in the ‘3d transitional group’ HEAs (possessing main components of V, Cr, Mn, Fe, Co, Ni, Cu) through the tuning of phase stability. Hence, inspired by these developments, a new design strategy for IVB element-based ductile RHEAs was proposed and investigated in the current research.