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Across biological scales, gene-regulatory networks employ autorepression (negative feedback) to maintain homeostasis and minimize failure from aberrant expression. Here, we present a proof of concept that disrupting transcriptional negative feedback dysregulates viral gene expression to therapeutically inhibit replication and confers a high evolutionary barrier to resistance. We find that nucleic-acid decoys mimicking cis -regulatory sites act as "feedback disruptors," break homeostasis, and increase viral transcription factors to cytotoxic levels (termed "open-loop lethality"). Feedback disruptors against herpesviruses reduced viral replication >2-logs without activating innate immunity, showed sub-nM IC 50 , synergized with standard-of-care antivirals, and inhibited virus replication in mice. In contrast to approved antivirals where resistance rapidly emerged, no feedback-disruptor escape mutants evolved in long-term cultures. For SARS-CoV-2, disruption of a putative feedback circuit also generated open-loop lethality, reducing viral titers by >1-log. These results demonstrate that generating open-loop lethality, via negative-feedback disruption, may yield a class of antimicrobials with a high genetic barrier to resistance. [Display omitted] • Transcriptional negative-feedback loops can be disrupted by cis -regulatory decoys • Feedback disruption raises expression levels generating "open-loop lethality" • Open-loop lethality inhibits viral replication in DNA and RNA viruses • Open-loop lethality exhibits a high barrier to the evolution of resistance Interference with viral negative feedback loops results in overexpression of cytotoxic viral proteins and host cell death, presenting an approach to antiviral therapy with a high barrier to the evolution of resistance. [ABSTRACT FROM AUTHOR]