Appropriate genetic parameters are essential for accurate selection of animals with improved genetic merit for economically important traits. In recent years, Merino breeders have tended to record animals earlier in life making it important to characterise post-weaning measurements. Additionally, genomic information is used in Australian Merino genetic evaluations to obtain more accurate estimations of genetic merit using single-step GBLUP, utilising a weighting factor to partition polygenic and genomic variance, hereby referred to as lambda (λ). This study aimed to estimate genetic parameters and lambda values for production traits measured at the post-weaning stage in Merino sheep. Phenotypic records were obtained at the post-weaning stage for weight (PWT), eye muscle depth (PEMD), fat depth (PFAT), greasy fleece weight (PGFW), clean fleece weight (PCFW), fibre diameter (PFD), fibre diameter coefficient of variation (PDCV), and staple length (PSL). Genetic parameters were estimated with univariate and bivariate analyses, while a genomic REML analysis was performed to calculate the lambda value for each trait. Moderate to high heritability estimates were observed, ranging between 0.25 to 0.56. Genetic correlations were moderately positive between PWT and PCFW, PGFW, PFD, and PSL and negative for PDCV. Lambda values were on average (0.64) slightly higher than the current value used for genomic evaluation (λ = 0.5) and ranged from 0.51 to 0.90. Genetic parameters reported in this study are generally consistent with previous studies and will be used to update the genetic parameters used by Sheep Genetics for the MERINOSELECT analyses.