A general approach to the construction of conservation laws for nonholonomic nonconservative dynamical systems in the event space was presented. Firstly, the differential equations of notion of systems are written, and the definition of integrating factors is given. Next, the necessary conditions for the existence of the conserved quantities are studied in detail. Finally, the existence theorem and its converse of conserved quantities for the nonholonomic nonconservative dynamical systems in the event space are established, and an example is given to illustrate the application of the result.