The aim of the study is to assess the impact of digitalisation, institutional transparency, and tax burden on the scale of the shadow economy in European Union (EU) countries in order to formulate strategic guidelines for Ukraine. The study employed correlation analysis, multiple regression analysis, robustness testing, and logical structure analysis. The results revealed that an increase in the Corruption Perceptions Index (CPI) by one point reduces the share of the shadow economy by 0.2604 percentage points (p = 0.0026), highlighting the critical role of institutional transparency and anti-corruption policy in the de-shadowing process. Tax burden demonstrated a positive and statistically significant relationship with the shadow economy (coefficient = 0.1843; p = 0.0125), indicating that excessive fiscal pressure may stimulate informal economic activity. The E-Government Development Index (EGDI) retained a positive but only marginally significant effect (coefficient = 50.3170; p = 0.0667), suggesting that digitalisation becomes effective primarily when embedded in public administration systems. In contrast, the overall level of digital development measured by DESI was not statistically significant after controlling for institutional and fiscal factors (coefficient = −0.2476; p = 0.1037). The constructed multifactor model demonstrated high explanatory power (R² = 0.8503), while robustness analysis confirmed the stability of the core findings across alternative model specifications. The results indicate that digitalisation alone is insufficient to reduce informality and that its effectiveness depends on institutional quality and balanced fiscal policy. The practical value of the study lies in identifying policy directions for Ukraine, including the expansion of e-government tools, digital tax administration, integrated data analytics, and anti-corruption measures aimed at reducing the shadow economy.