Significance Regulatory T (Treg) cells have been highlighted for their central function in limiting the severity of autoimmune diseases such as multiple sclerosis (MS). To date, the anatomical location and timing of this Treg cell–mediated suppression are unknown. In this report, in a mouse model of MS, we demonstrate that Treg cells inhibit the pathogenic process directly in the central nervous system during established disease, rather than in the presymptomatic phase. This protective function requires the surface expression of TNF receptor 2 by Treg cells, as its genetic ablation or antibody-mediated blockade worsens disease symptoms. Our data reveal a unique function of Treg cells in autoimmunity and highlight TNFR2 as a promising therapeutic target.