In this innovative research, a novel series of thiazolidin-4-one analogues having a 1,3,4-oxadiazole/thiadiazole moiety were derived and the structures of all the newly obtained molecules were established using different physicochemical and analytical means (1H-NMR, FTIR, mass spectra, and elemental analyses). The synthesized molecules were then investigated for their antiproliferative, antimicrobial, and antioxidant potential. The cytotoxicity screening studies revealed that analogues D-1, D-6, D-15, and D-16 possessed comparable efficacy, within the IC50range (1 to 7 μM), when taking doxorubicin as a reference drug (IC50= 0.5 μM). The antimicrobial activity was assessed using different Gram-(+) and Gram-(−) bacterial and fungal strains and the results revealed that molecules D-2, D-4, D-6, D-19, and D-20 possessed potent activity against selective strains of microbes with MIC ranges of 3.58 to 8.74 µM. The antioxidant evaluation was performed using the DPPH assay and the screening results revealed that analogue D-16 was the most potent derivative (IC50= 22.3 µM) when compared with the positive control, ascorbic acid (IC50= 111.6 µM). Structure–activity relationship (SAR) studies of the synthesized novel derivatives revealed that para-substituted halogen and hydroxy derivatives have remarkable potential against the MCF-7 cancer cell line and antioxidant potential. Similarly, electron-withdrawing groups (Cl/NO2) and -donating groups at the para position possess moderate to promising antimicrobial potential.