Selenium (Se)-enriched vegetables are promising dietary sources of Se, which provides beneficial biological effects in humans. In this study, we investigated the effects of foliar application of Se on hydroponically grown multi-leaf green (V1) and red (V2) lettuce plants. Three selenate (SeIV) amendment levels were evaluated for their influence on plant growth, elemental composition and radical scavenging capacity. Lettuce heads biofortified with 0.598 mg Se plant−1 accumulated 19.6–23.6 and 14.9–17.6 μg Se g−1 DM in the multi-leaf green (V1) and red (V2) lettuce plants, respectively. The accumulated Se levels can contribute significantly to the recommended dietary allowance of 70 µg day−1 for adult men and 60 µg day−1 for adult women. Accordingly, both V1 and V2 lettuce cultivars grown under the Se3 foliar application condition can cover the daily requirement for adult men by approximately 100% and 85% to 100%, respectively, by consuming 75–90 g or 100 g fresh weight from V1 or V2, respectively. The ABTS radical scavenging potential of green lettuce was induced at Se2 and Se3 foliar application levels, where the IC50 was 1.124 ± 0.09 μg mL−1 at Se0 and improved to 0.795 ± 0.03 and 0.697 ± 0.01 μg mL−1, respectively. There was no cytotoxicity against Vero kidney cells among all treated lettuce plants at the highest concentration tested of 1 mg/mL. Finally, a further focused investigation of the metabolic profile of lettuce plants under varied Se levels needs to be investigated in future studies.