Photopolymerization-based 3D printing process is typically conducted using nonliving free radical polymerization, which leads to fabrication of immutable materials. An alternative 3D printing of polymeric materials using trithiocarbonate (TTC) reversible addition-fragmentation chain transfer (RAFT) agents has always been a challenge for material and polymer scientists. Herein we report the first 3D printing of RAFT-based formulations that can be conducted fully open to air using standard digital light processing (DLP) 3D printer and under mild conditions of visible light at blue (λ max = 483 nm, 4.16 mW/cm2) or green (λ max = 532 nm, 0.48 mW/cm2) wavelength. Our approach is based on activation of TTC RAFT agents using eosin Y (EY) as a photoinduced electron-transfer (PET) catalyst in the presence of a reducing agent (tertiary amine), which facilitated oxygen tolerant 3D printing process via a reductive PET initiation mechanism. Re-activation of the TTCs present within the polymer networks enables post-printing monomer insertion into the outer layers of an already printed dormant object under second RAFT process, which provides a new pathway to design a more complex 3D printing. To our best knowledge, this is the first example of open-to-air PET-RAFT facilitated 3D printing of polymeric materials. We believe that our strategy is a significant step forward in the field of 3D printing.