Magnetization hysteresis loops and magnetic susceptibility were measured from Mg0.9Ti1.1O3 and Mg0.88Ti 1.12O3 samples. The hysteresis loops revealed that the ferromagnetic transition occurs at or below 260 K. The magnetization did not reach saturation up to 70 kOe at 5 K. In contrast, stoichiometric MgTiO 3, consisting of closed-shell ions, does not exhibit magnetic ordering. Combined magnetic susceptibility measurements, X-ray diffraction, X-ray photoelectron spectroscopy, and spin-polarized density-functional theory computations show that the ferromagnetism is due to the conduction electrons, which are responsible for the semimetallic nature of the titanium-rich magnesium titanate Mg1-xTi1+xO3 solid solution. Excess Ti at the Mg-O cation layer results in a partially occupied band at the conduction band edge. This in turn shows that the magnetic properties can be controlled by a transition metal element substitution in a cation layer, which is a technological advantage.