The characteristics of three-dimensional ion-acoustic solitary waves (IASWs) have been investigated in a magnetized plasma including ions, nonthermaly dispersed electrons and positrons. The reductive perturbation technique (RPT) is used to develop the Zakharov–Kuznetsov (ZK) equation for observing ion-acoustic wave structure, and a soliton solution is obtained by using the tangent hyperbolic (tanh) method. The influence of various parameters on the soliton profile, such as nonthermal parameters for electrons and positrons, density ratios of positron–electron and ion–electron, and temperature ratio of electron–positron, is presented graphically.