The fall armyworm (Spodoptera frugiperda) is a significant agricultural pest with a broad host range and adaptability, posing challenges to pest management worldwide. To elucidate the molecular mechanisms underpinning their development and resilience, we performed a comprehensive transcriptomic analysis across nine developmental stages, spanning from the 1st instar larvae to adult forms. Utilizing differential expression analysis and time-series clustering, we identified 6,834 differentially expressed genes (DEGs), uncovering key stage-specific expression patterns. Notably, 3,072 stage-specific genes (SSGs) were defined using the Tau index, highlighting their roles in development and physiological adaptation. Functional enrichment revealed that the 6th instar stage prioritizes pathways related to growth and tissue remodeling, while adult males emphasize reproductive and sensory functions. Furthermore, we characterized 104 cytochrome P450 (P450) genes, showcasing distinct temporal expression patterns critical for detoxification and metabolic processes. A tandem array of P450 genes on chromosome 13 was identified, suggesting a coordinated mechanism enhancing insecticide resistance. Our findings shed light on the complex genetic regulation that facilitates the developmental transitions and adaptive capabilities of S. frugiperda. These insights offer potential molecular targets for innovative pest management strategies aimed at mitigating the widespread impact of this pest.