This study investigated the effects of supplemental far-red (FR) lighting on photomorphogenic responses and productivity in Crepidiastrum denticulatum, a native Korean medicinal plant, grown in vertical farms using artificial lighting. Photomorphogenesis refers to the growth and developmental changes in plants in response to light signals. The background light sources were white (W) light-emitting diodes (LEDs) and red, green, and blue (RGB) mixed LEDs. Supplemental FR lighting was added to both background light sources at a red to far-red (R/FR) ratio of 1.2, referred to as W + FR and RGB + FR treatments. Fluorescent light (FL) served as a control. Plants were cultivated under five light treatments for six weeks in a controlled environment with an air temperature 20°C, relative humidity 60%, photosynthetic photon flux density 200 µmol·m–2·s–1, photoperiod 16 h·d–1, and CO2 concentration 1000 µmol·mol–1. The addition of supplemental FR lighting significantly influenced photomorphogenic response, enhancing plant growth by increasing leaf area and biomass by up to 2.7 times compared to the control. Canopy net photosynthetic rates were significantly increased by supplemental FR lighting, especially under the W + FR treatment. While total phenolic content and antioxidant capacity per unit dry weight were highest under the RGB treatment, the W + FR treatment exhibited the highest accumulation of these metabolites per shoot due to increased biomass. These findings suggested that supplemental FR light effectively modulates photomorphogenic responses, enhancing growth and bioactive compound accumulation in C. denticulatum. The results indicate the potential of manipulating light quality, particularly by adding FR light, to optimize vertical farming practices for medicinal plants.