A unique population of Foxp3⁺CD4⁺ regulatory T (T_reg) cells resides in visceral adipose tissue (VAT) of lean mice, especially in the epididymal fat depot. VAT T_regs are unusual in their very high representation within the CD4⁺ T-cell compartment, their transcriptome, and their repertoire of antigen-specific T-cell receptors. They are important regulators of local and systemic inflammation and metabolism. The overall goal of this study was to learn how the VAT T_reg transcriptome adapts to different stimuli; in particular, its response to aging in lean mice, to metabolic perturbations associated with obesity, and to certain signaling events routed through PPARγ, the “master-regulator” of adipocyte differentiation. We show that the VAT T_reg signature is imposed early in life, well before age-dependent expansion of the adipose-tissue T_reg population. VAT T_regs in obese mice lose the signature typical of lean individuals but gain an additional set of over- and underrepresented transcripts. This obese mouse VAT T_reg signature depends on phosphorylation of the serine residue at position 273 of PPARγ, in striking parallel to a pathway recently elucidated in adipocytes. These findings are important to consider in designing drugs to target type 2 diabetes and other features of the “metabolic syndrome.”