Introduction: How entrenched political parties shape social policy remains a central question. This paper explores whether institutionalized parties — those with stable linkages to broad social groups, not captured by special interests, and constrained by strong executive checks — foster more universal welfare systems.

Data & Methods: We employ original metrics of party institutionalization alongside established indicators of welfare state features across diverse country contexts.

Key Findings: This study reveals, after accounting for fixed effects like electoral system structure or union influence, that connections between party organizations and broader society correlate strongly with comprehensive welfare systems. The effect is particularly pronounced in democracies but also exists within autocratic regimes.

Mechanism Insight: When examining specific pathways, institutionalized parties' stable social linkages emerge as a significant motivator for expansive welfare programs — though not the sole driver of such policy outcomes.

Real-World Relevance: These findings suggest political party reforms in emerging democracies might carry implications beyond electoral stability alone.