An electrode catalyst according to the present disclosure includes: a mesoporous material; and catalyst metal particles supported at least within the mesoporous material and including platinum and a metal different from platinum. The mesoporous material has mesopores with a mode radius of greater than or equal to 1 nm and less than or equal to 25 nm and a pore volume of greater than or equal to 1.0 cm3/g and less than or equal to 3.0 cm3/g. The catalyst metal is represented by the chemical formula PtxCo1-yNiy, x is greater than or equal to 1 and less than or equal to 3 and y is greater than or equal to 0.20 and less than or equal to 0.47. The catalyst metal particles include an L10 phase.