Bisurea anions have shown high activity and selectivity in the ring-opening polymerization (ROP) of cyclic esters. By integrating density functional theory modeling with experimental investigations, we elucidate the key mechanistic features underlying their catalytic behavior in the ROP of ε-caprolactone (ε-CL). Our study reveals that hydrogen-bond cooperativity between the urea groups, enforced by an ortho-phenylene linker, generates a semi-rigid catalytic pocket that is central to both activity and selectivity. The K⁺ counterion further stabilizes this architecture by reinforcing catalyst preorganization and substrate binding. This cooperative structural arrangement efficiently promotes ε-CL polymerization while suppressing transesterification pathways. Collectively, these insights establish design principles for next-generation hydrogen-bonding organocatalysts for ROP.