This work proposes that Planck’s constant (hh) is not an independent fundamental quantity but a derived parameter determined by the invariance condition of the Principle of Unified Cosmodynamics (PUC). The PUC invariant links the expansion of space and time, fixing the Planck time and thereby defining hh. This cosmological perspective connects the microscopic quantum scale directly to macroscopic spacetime dynamics. The paper further shows how PUC naturally suppresses vacuum energy through regression memory effects, resolves the cosmological constant problem, and explains the Higgs vacuum expectation value without fine-tuning. Overall, PUC provides a unified framework for the origin of Planck’s constant and addresses major open questions in cosmology and particle physics.