An excellent nonlinear optical (NLO) material should satisfy many critical requirements simultaneously. How to balance all the requirements is a challenge, as they cause contradictory demands on structural attributes. Here, we use a high entropy strategy to integrate the advantages of ZnSe for a large NLO coefficient and a planar [InSe3]3− functional motif for phase matching. The resulting Ba6In6Zn4Se19 crystal shows excellent comprehensive NLO properties, i.e. a large effective NLO coefficient (2 × AgGaS2), a high laser induced damage threshold (LIDT, 15.5 × AgGaS2), a wide transmission range (0.52–22.5 μm), and an increased birefringence (Δn = 0.098) for phase matching. Theoretical calculations indicate that planar [InSe3]3− is an effective NLO functional motif for tuning birefringence and the “cocktail effect” realized via the high entropy strategy is important to improve the overall NLO performance. This study provides a promising way of developing new NLO materials with excellent comprehensive performance.