Abstract. Using a superfield formulation of extended phase space, we propose a new form of the Hamiltonian action functional. A remarkable feature of this construction is that it directly leads to the BV master action on phase space. Conversely, superspace can be used to construct nilpotent BRST charges directly from solutions to the classical Lagrangian Master Equation. We comment on the relation between these constructions and the specific master action proposal of Alexandrov, Kontsevich, Schwarz and Zaboronsky.