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CRISPR technologies have begun to revolutionize T cell therapies; however, conventional CRISPR-Cas9 genome-editing tools are limited in their safety, efficacy, and scope. To address these challenges, we developed multiplexed effector guide arrays (MEGA), a platform for programmable and scalable regulation of the T cell transcriptome using the RNA-guided, RNA-targeting activity of CRISPR-Cas13d. MEGA enables quantitative, reversible, and massively multiplexed gene knockdown in primary human T cells without targeting or cutting genomic DNA. Applying MEGA to a model of CAR T cell exhaustion, we robustly suppressed inhibitory receptor upregulation and uncovered paired regulators of T cell function through combinatorial CRISPR screening. We additionally implemented druggable regulation of MEGA to control CAR activation in a receptor-independent manner. Lastly, MEGA enabled multiplexed disruption of immunoregulatory metabolic pathways to enhance CAR T cell fitness and anti-tumor activity in vitro and in vivo. MEGA offers a versatile synthetic toolkit for applications in cancer immunotherapy and beyond., Competing Interests: Declaration of interests The authors have filed a patent related to this work. E.S. consults for Lyell Immunopharma, Lepton Pharmaceuticals, and Galaria. C.L.M. is a cofounder of Lyell Immunopharma, CARGO Therapeutics, and Link Cell Therapies and consults for Lyell, CARGO, Link, Apricity, Nektar, Immatics, Ensoma, Mammoth, Glaxo Smith Kline, Bristol Myers Squibb, and RedTree Capital. L.S.Q. is a founder of Epic Bio and scientific advisor of Laboratory of Genomic Research and Kytopen Corp., (Copyright © 2024 Elsevier Inc. All rights reserved.)