Saposhnikovia divaricata (Turcz.) Schischk is an important medicinal species used for the production of Radix Saposhnikoviae in East Asia. Since its introduction into Vietnam, comprehensive field evaluation of its agronomic performance and phytochemical quality under local ecological conditions remains limited. This study assessed the agro-biological characteristics, yield performance, and medicinal root quality of a selected S. divaricata germplasm introduced from China and cultivated at the Tam Dao Medicinal Plant Research Station, Phu Tho Province, northern Vietnam. The experiment was conducted during the 2023–2024 growing season using a randomized complete block design with three replications, comparing the selected line (PP2) with the original imported cultivar (PP1). The selected germplasm showed typical morphological traits and consistent performance under the tested conditions. Significant improvements (P < 0.05) were observed in root length and dry root weight relative to the control. Mean plant height, root length, root diameter, and dry root weight reached 40.0 cm, 23.8 cm, 1.8 cm, and 40.5 g/plant, respectively, resulting in an estimated yield of 966.7 kg/ha High-performance liquid chromatography with diode-array detection (HPLC-DAD) showed clear and well-resolved peaks of prim-O-glucosylcimifugin and 5-O-methylvisamminoside. Total chromone content reached 1.00%, comprising 5-O-methylvisamminoside (0.58%) and prim-O-glucosylcimifugin (0.42%), substantially exceeding the pharmacopoeial minimum requirement (0.24%, dry weight basis). Overall, the selected germplasm combines improved yield-related traits with high medicinal root quality, supporting its potential for cultivation under northern Vietnam conditions.