<p>This paper introduces a semi-analytical method to investigate the free and forced vibration of a sandwich plate in thermal environment under magnetic and electric fields and subjected to uniformly distributed loading. The sandwich plate consists of a core layer made of three-phase composite material and two facesheets made of magneto-electro-elastic (MEE) material. The magnetic and electric potentials are assumed to be a combination of trigonometric and linear functions to satisfy Maxwell’s equations. Analytical expressions for the material properties of the three-phase composite core are determined from the volume fraction of the matrix, reinforcing fibers and particles. The governing equations of motion for the MEE sandwich plate are derived using Hamilton’s principle and Reddy’s higher order deformation plate theory. Galerkin and Runge–Kutta methods are employed to obtain the natural frequency, phase plane trajectory and dynamic response of the sandwich plate. Numericalf examples are conducted to assess the influences of various parameters including geometrical properties, fiber and particle volume fraction, temperature increment, magnetic and electric potentials and elastic foundations in detail. The results of this paper can be effectively applied for the precise design and development of three-phase composite and smart structures.</p>