Spontaneous chiral symmetry breaking remains a fascination in chemistry, biology, materials science, and even astronomy. Chiral symmetry breaking usually requires intrinsic molecular chirality or extrinsic chiral sources but remains rare in nonchiral systems. Here, we reveal a ubiquitous, entropy-driven chiral symmetry breaking mechanism observed in 22 out of 35 conjugated polymers in the absence of any chiral source─a phenomenon overlooked for decades. Chiral assemblies spontaneously occur through liquid-liquid phase separation (LLPS) of lyotropic mesophases from isotropic solutions upon a concentration increase. Machine learning identifies the underpinning molecular features validated by further molecular design. The universality of this phenomenon hints at a possible link between LLPS and chiral symmetry breaking in the origin of life, while paving the way for an emerging frontier of chiral electronics.