ABSTRACT Cambarus veteranus Faxon 1914 (Guyandotte River Crayfish), is a federally endangered, narrow endemic. A 2 year life history study was initiated for C. veteranus in Clear Fork of the Guyandotte River, Wyoming County, West Virginia, USA. Monthly collections began June 2017 and continued through May 2019. Specimens, regardless of species, were collected, sexed, and moult stage determined. Monthly length frequency distributions identified five age‐size classes for the population assessed. Form I males were collected all months sampled and reached their highest density in April. Mature females with signs of glair were captured nearly every month but reached their highest density in June. A single female bearing pleopodal eggs was captured in August and females with Stage 4 juveniles were subsequently observed in September and November. Females overwintering with juveniles were evidenced by females captured with Stage 4 juveniles in March for both years sampled. Two synchronous moulting events were identified for the population around seasonal thermal shifts with the highest frequency of moulting individuals observed in May and September. Our exploration of discontinuous growth utilised non‐traditional growth models due to the small sample sizes per age‐size class. The results corroborated the expected growth for Cambarus crayfish. Differences in timing for ontogenic allometric shifts in growth were observed between males and females and provided insight into when resources shift from general growth allocation to growth required for reproduction. This study employed unique life history methodologies, rarely applied to crayfish, to provide information essential for the successful conservation of this endangered species, while enabling comparisons with closely related species often assumed to share similar life history strategies.