Abstract: I discuss in detail the emergence of a metastable inflationary vacuum within Chern-Simons (CS) Gravity, which contains axion fields coupled to gravitational anomalies. First, I explain the emergence of CS gravity as a consistent effective low-energy gravitational field theory of strings, and then I demonstrate the appearance of (complex) condensates of CS gravitational anomaly due to chiral gravitational waves. I place this discussion in the context of a string-inspired running vacuum model (RVM) cosmology. I explain carefully the passage from a pre-inflationary axion-dominated stiff era to inflation in such a framework. Specifically, I demonstrate how an unbounded linear-axion potential emerges as a result of the CS condensate, and how the resulting theory  acquires meaning as an inflationary RVM of inflation, with a graceful exit from it and reheating, without the need for fundamental inflatons.  Moreover, on assuming the existence of periodic modulations of the axion potential, induced by non-perturbative effects (instantons), I evaluate the slow-roll parameters associated with the axion-field cosmic flow, and demonstrate agreement with the data, upon fixing the magnitude of the instantons energy scale and the size of their (Euclidean) actions.