Hemp and linseed are nutritionally valuable commodities that exhibit considerable varietal differences in composition. Nutrient composition was evaluated in 12 hemp and 11 linseed varieties, including commercially cultivated varieties from the EU Common Catalogue and newly bred lines, to assess varietal variability. Field experiments were conducted under uniform agronomic conditions in the Czech Republic during a single growing season using field-block samples. Analyses included proximate composition (dry matter, crude protein, fat, fiber, ash), fatty acid and amino acid profiles, carotenoids, vitamins, and cannabinoid content. Statistical evaluation was performed using a General Linear Model with Duncan’s multiple range test (p < 0.05). Significant differences were observed across most parameters, indicating substantial inter-varietal variability under the experimental conditions. Fat content ranged from approximately 200 to 377 g/kg in both oilseeds, with lipids dominated by polyunsaturated fatty acids, particularly linoleic (n-6) and α-linolenic (n-3) acids. Hemp and linseed show potential as alternative plant protein sources in animal nutrition, but further digestibility and feeding studies are needed to confirm their suitability as partial soybean meal substitutes. Varietal selection may contribute to improved nutritional quality while influencing levels of undesirable constituents such as Δ9-THC in hemp.