Instagram’s popularity has raised concern about its problematic use. However, no validated scales assessing Instagram addiction exist in the Indian context. The present study evaluated the psychometric properties of the 15-item Instagram Addiction Scale (IAS-15) among Indian adults. In total, 301 participants (Mage = 22.89 years) were recruited using a convenience sampling technique. Confirmatory factor analysis indicated that the two components of the IAS-15, social effect and compulsion, had suitable factor loadings: CMIN/DF (chi-square/degree of freedom) = 2.531, GFI (goodness of fit index) = 0.903, IFI (incremental fit index) = 0.965, TLI (Tucker-Lewis index) = 0.958, CFI (comparative fit index) = 0.965, and RMSEA (root mean square error of approximation) = 0.071. This was further improved by drawing covariances between theoretically linked items (CMIN/DF = 2.273, GFI = 0.916, IFI = 0.972, TLI = 0.965, CFI = 0.971, and RMSEA = 0.065). Strong convergent validity with a significant and positive correlation with social media addiction (r = 0.899), and strong concurrent validity with depression (r = 0.778), anxiety (r = 0.777), stress (r = 0.815), and negative correlations with self-esteem (r = −0.635) were observed. The IAS-15 demonstrated excellent internal consistency with Cronbach’s alpha (α) and McDonald’s omega (ω) coefficients of reliability for the overall scale (α = 0.962 and ω = 0.963) and its two subscales, social effect (α = 0.941 and ω = 0.942) and compulsion (α = 0.922 and ω = 0.922). Findings confirm that the IAS-15 is a valid and reliable instrument for assessing Instagram addiction among Indian adults.