As consumer interest in functional foods increases, so does the demand for nutrient-dense and visually appealing vegetables. Swiss chard (Beta vulgaris subsp. cicla), recognized for its colorful petioles and nutritional richness, stands as a promising candidate. This study aimed to evaluate the phytochemical composition of baby leafy greens from four Swiss chard varieties (white, yellow, pink, and orange) cultivated using a soilless system under semi-controlled indoor conditions. Plants were grown in a walk-in growth chamber equipped with LED lighting. Seeds were sown in vermiculite-filled trays, kept in darkness for four days to induce germination, and irrigated with a 3:1:6 NPK nutrient solution. Seven days after sowing, uniform and healthy seedlings from each variety were transplanted into individual rockwool cubes and cultivated under a 14/10 h light/dark photoperiod, with temperatures ranging from 20 to 25 °C and relative humidity around 60%. After 27 days of growth post-transplantation, baby leafy greens were harvested for phytochemical analysis using high-performance liquid chromatography with diode array detection and electrospray ionization mass spectrometry. In total, up to 11 phenolic compounds, 4 betalains, and 10 saponins were identified among the different varieties. Pink Swiss chard baby greens exhibited the highest phenolic compound content (12.15 mg/g dw). The white variety was the only one in which betalains were detected (1.99 mg/g dw), comprising one betacyanin and three betaxanthins. The yellow variety presented the highest saponin concentrations (911.1 µg/g dw). These findings reveal distinct phytochemical profiles among Swiss chard baby leaf varieties, emphasizing their chemical diversity and supporting their potential as functional foods rich in bioactive compounds.