A new theoretical concept of an electrically controllable single-electron spin filter (polarizator) based on the exchange interaction in the system of interacting quantum dots or impurity atoms is proposed. The sign of the spin polarization of the current flowing through the device can be effectively controlled in two ways (i) by changing the applied bias and (ii) by tuning the tunnel coupling via an external gate. The minimal realization involves three bound state levels coupled to the contact leads. One of these levels is occupied by a single electron with a certain spin and the two-electron occupation is prohibited by a strong on-site Coulomb repulsion. Interestingly, while the spin polarization of this state is fixed, the sign of the single-electron current spin polarization flowing between the contacts through two consistent bound state levels can be switched. •A new theoretical concept of an electrically controllable single-electron spin filter is proposed.•The presence of both exchange interaction and on-site Coulomb repulsion is important.•Spin-filtering can be organized by changing the applied bias or by tuning the tunnel coupling via an external gate.•The considered phenomena are sensitive to electron correlations giving an experimental access to the many-body phenomena.•The obtained results open the possibility for precise control of tunneling current spin polarization.