Solute segregation to stacking faults (also known as Suzuki segregation) has been employed to stabilize the planar defects to design desired plastic deformation mechanisms in Co- and Ni-based alloys and superalloys. High-temperature deformations of the Co/Ni alloys and superalloys are usually controlled by the dislocation/stacking fault interactions, which can be strengthened by alloying elements. However, the fundamental driving forces for solute segregation to planar defects are not well understood for transition metals in the Co and Ni alloys. The solute segregation behaviors in intrinsic stacking faults (ISF) and the electronic origin of the segregation remain unclear in face-centered cubic Co- and Ni-alloys. The segregation energies calculated by thermodynamic models of bulk materials may not satisfy the demands for accurate prediction of segregation. We first predicted the solute-ISF interaction energy for 3d, 4d, and 5d transition metal elements in FCC Co and Ni, see Figure 1, using density functional theory. The Ni-Co and Ni-Ti FCC binary systems were experimentally investigated to discuss the effects of solutes on segregation. We further revealed that the driving force of segregation can be attributed to the confluence of the local atomic distortions, charge density redistribution, electron orbital interactions, and local magnetic interactions between the solute and the solvent atoms. The predicted interaction energies can be utilized in future alloy design efforts to improve mechanical properties via Suzuki segregation to planar defects.