We show that in oxide thin films of spiral antiferromagnetic orthorhombic TbMnO ₃ , ferromagnetism emerges resulting from epitaxially induced strain. The unit cell volume can be tuned (contracting up to a 2%) by varying thickness and deposition conditions; it is found that the ferromagnetic response correlates with the unit cell deformation. Such effect of strain on the magnetic properties turns out to be similar to that occurring in collinear orthorhombic antiferromagnets such as YMnO ₃ . Owing to the intimate relationship between magnetic order and ferroelectricity in TbMnO ₃ these results may provide a new route to induce magnetoelectric coupling and tailor their ferroelectric response.