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Ligation of retinoic acid receptor alpha (RARα) by RA promotes varied transcriptional programs associated with immune activation and tolerance, but genetic deletion approaches suggest the impact of RARα on TCR signaling. Here, we examined whether RARα would exert roles beyond transcriptional regulation. Specific deletion of the nuclear isoform of RARα revealed an RARα isoform in the cytoplasm of T cells. Extranuclear RARα was rapidly phosphorylated upon TCR stimulation and recruited to the TCR signalosome. RA interfered with extranuclear RARα signaling, causing suboptimal TCR activation while enhancing FOXP3+ regulatory T cell conversion. TCR activation induced the expression of CRABP2, which translocates RA to the nucleus. Deletion of Crabp2 led to increased RA in the cytoplasm and interfered with signalosome-RARα, resulting in impaired anti-pathogen immunity and suppressed autoimmune disease. Our findings underscore the significance of subcellular RA/RARα signaling in T cells and identify extranuclear RARα as a component of the TCR signalosome and a determinant of immune responses. [Display omitted] • A cytoplasmic isoform of RARα (cRARα) is activated by the TCR and binds TCR-ZAP-70 • RA counteracts cRARα for suboptimal T cell activation and enhanced Treg conversion • Effective cRARα-TCR signaling induces CRABP2 for RA translocation to the nucleus • Defects in CRABP2 expression reduce anti-pathogen immunity and autoimmune disease Nuclear retinoic acid receptor alpha (RARα) regulates gene transcription upon the binding of retinoic acid (RA). Larange, Takazawa, Kakugawa, Thiault et al. identify an RARα isoform in the cytoplasm of T cells (cRARα) and reveal that cRARα binds the TCR-ZAP-70 complex, thereby regulating T cell proliferation and effector differentiation. RA counteracts TCR-engaged RARα, resulting in suboptimal TCR activation but enhanced Treg cell differentiation. [ABSTRACT FROM AUTHOR]