Carbon fibre-reinforced polymers are increasingly employed in thick, load-bearing structures across several sectors. However, their potential is hindered by manufacturing-induced defects such as thermal overshoot, residual stresses, and uneven cure, which compromise performance, dimensional stability, and process reliability. Conventional mitigation strategies optimise curing cycles but become inefficient for thick parts due to excessively long cure times. This limitation calls for alternative manufacturing routes. This thesis investigates stepwise curing as a defect-mitigation strategy in thick carbon/epoxy composites, involving partial reaction of the thermoset matrix prior to deposition, then further reaction during tow/layer deposition and compaction, and finally post-curing. This concept is adapted both to prepreg lay-up and additive manufacturing by tow deposition. The objectives were thus to: assess the influence of stepwise curing on internal strain and warpage; quantify how tow-by-tow curing affects thermal overshoot, residual stress, and process time; and evaluate the effect of pre-curing and in-situ consolidation on the interlaminar performance of composites. An integrated experimental-numerical approach was adopted. Distributed fibre optic sensors enabled real-time strain monitoring during curing of thin and thick laminates. Thermo-mechanical simulations incorporating cure kinetics and evolving material properties were developed to predict the influence of pre-cure level, deposition speed, and heat input on stress generation, overshoot, and cure time. A proof-of-concept winding line was also built to manufacture curved laminates under controlled pre-cure and compaction conditions, followed by mechanical and microstructural characterisation. Experimental results on thin laminates showed that pre-curing plies up to 50% conversion reduced internal strain and warpage by 31% and 14%, corresponding to 94 µe and 11 MPa reductions compared to composites made from uncured plies. In thick laminates, pre-curing to 28% conversion lowered peak temperature and residual strain by 29% and 17% (166 µe and 24 MPa reductions). Numerical simulations confirmed that tow-by-tow stepwise curing could reduce the exotherm by up to 92% and through-thickness stress gradients by 65%, compared to batch curing, while enabling faster cycles. Finally, tow-wound curved laminates produced from partially pre-cured tows showed low void content < 2% and stable interlaminar performance with an average interlaminar shear strength of 56±4 MPa and stable fracture toughness around a pre-cracked energy release rate of 462±102 J m-2, confirming that pre-curing below gelation does not impair interlaminar properties. The findings demonstrate that the proposed manufacturing strategy effectively mitigates cure-induced defects in thick composites, providing experimental and numerical evidence of defect reduction via stepwise curing. The work establishes partial pre-curing as an effective method for controlling stress gradients, thermal overshoot, and residual strain, thereby enhancing dimensional accuracy, structural reliability, and manufacturing efficiency. This research opens opportunities for new reliable and automated composite manufacturing processes based on pre-cured components and highlights the potential of coupling real-time monitoring with predictive simulations for adaptive cure control and performance assessment throughout manufacturing and service life.