Follicular regulatory T (Tfr) cells are a regulatory T cell subset that controls antibody production by inhibiting T follicular helper (Tfh)-mediated help to B cells. Tfh and Tfr cells possess opposing functions suggesting unique programming. Here we elucidated the transcriptional program controlling Tfr suppressive function. We found that Tfr cells have a program for suppressive function fine-tuned by tissue microenvironment. The transcription factor FoxP3 and chromatin-modifying enzyme EZH2 are essential for this transcriptional program but regulate the program in distinct ways. FoxP3 modifies the Tfh program to induce a Tfr-like functional state, demonstrating that Tfr cells coopt the Tfh program for suppression. Importantly, we identified a Tfr cell population that loses the Tfr program to become "ex-Tfr" cells with altered functionality. These dysfunctional ex-Tfr cells may have roles in modulating pathogenic antibody responses. Taken together, our studies reveal mechanisms controlling the Tfr transcriptional program and how failure of these mechanisms leads to dysfunctional Tfr cells.