A series of 3-[3-substituted-5-mercapto-1,2,4-triazol-4-yl]-spiro-(indan-1′,2-thiazolidin)-4-ones 2 were designed for the purpose of searching for novel antimicrobial agents and have been synthesized conveniently in a single step with a three-component protocol in polyethylene (400) as green reaction media. Thus, the condensation reaction between indane-1-one; 4-amino-5-mercapto-1,2,4-triazoles and mercaptoacetic acid in polyethylene glycol (400) gave quantitatively and analytically pure titled compounds 2. The structure of synthesized compound 2 is based on spectral (IR, 1H-NMR, and 13C-NMR) as well elemental analyses. These compounds have been screened for their antibacterial, antifungal, and antitubercular activities. Some of them have showed significant inhibition on fungal and bacterial growth and antitubercular activity against Mycobacterium tuberculosis. The compounds 2a, 2d, and 2e display antifungal activity against Candida albicans [minimum inhibitory concentration (MIC) 3.13, 6.25 μg/mL] and antibacterial activity against Streptococcus pneumoniae (MIC 3.13 μg/mL) of the order of standard drugs tested under similar conditions, and compound 2a showed better antitubercular activity than other compounds against M. tuberculosis (H37Rv strain, MIC 12.5 μg/mL).