Regioregular poly(3-hexylthiophene), rr-P3HT, has been commonly synthesized using Grignard metathesis (GRIM) polymerization and is used as an active material for large area printing of various optoelectronic devices. Batch to batch reproducibility which is very crucial for the development of a large area printing technology for any material still remains one of the major challenges for bulk synthesis. This is due to the insolubility of the GRIM catalyst (1,3-bis(diphenylphosphino)propane nickel(II) chloride) in polymerization solvents. In this article, we have successfully developed a continuous-flow process for the ultrafast syntheses of rr-P3HT with high throughput and low polydispersity index (PDI). The key to success was the use of 3,4-ethylenedioxythiophene, EDOT, as an inert solvent for dissolving the GRIM catalyst. We could successfully carry out the flow syntheses of rr-P3HT at high concentration (500 mM monomer solution) with low PDI (~1.2) along with good batch to batch reproducibility and high throughput of 32.8 g per channel per hour for rr-P3HT. The combination of higher monomer concentration with ultrafast polymerization resulted in an efficient process for the large-scale syntheses of rr-P3HT with reduced chemical waste. Furthermore, the optical studies along with electrical characterization indicated better packing and higher charge carrier mobility as compared to the commercial samples with high polydispersity index.