AbstractInterface physics in oxides heterostructures is pivotal in material’s science. Domain walls (DWs) in ferroic systems are examples of naturally occurring interfaces, where order parameter of neighboring domains is modified and emerging properties may develop. Here we show that electric tuning of ferroelastic domain walls in SrTiO3leads to dramatic changes of the magnetic domain structure of a neighboring magnetic layer (La1/2Sr1/2MnO3) epitaxially clamped on a SrTiO3substrate. We show that the properties of the magnetic layer are intimately connected to the existence of polar regions at twin boundaries of SrTiO3, developing at "Equation missing", that can be electrically modulated. These findings illustrate that by exploiting the responsiveness of DWs nanoregions to external stimuli, even in absence of any domain contribution, prominent and adjustable macroscopic reactions of neighboring layers can be obtained. We conclude that polar DWs, known to exist in other materials, can be used to trigger tunable responses and may lead to new ways for the manipulation of interfacial emerging properties.