A new green methodology has been developed for the synthesis of a series of substituted 5-arylidene-2,4-thiazolidinediones (ATZDs) 3a-q through Knoevenagel condensation, using barium hydroxide as an efficient heterogeneous catalyst. All compounds were characterized by H-1 NMR, C-13 NMR, and HRMS spectroscopy. Additionally, seven compounds were analyzed by X-ray diffraction (XRD). Furthermore, some selected TZD derivatives were screened for their antioxidant activity using oxygen radical absorbance capacity (ORAC) assays. The results showed that five compounds exhibited excellent antioxidant properties, with ORAC values ranging from 4.73 TE to 6.31 TE, surpassing the reference antioxidants ferulic acid (3.70 TE) and melatonin (2.45 TE). Computational investigations based on the DFT method revealed that these compounds exert their antioxidant activity primarily through the HAT mechanism, preferentially from the OH bond rather than the NH bond. This study highlights the advantages of this methodology, providing products of high purity, with good yields and short reaction times, and proposes 5-arylidene-thiazolidine-2,4-dione derivatives as promising antioxidants.