  We derive a manifestly MHV Lagrangian for the N=4 supersymmetric Yang-Mills
theory in light-cone superspace. This is achieved by constructing a canonical
redefinition which maps the N=4 superfield and its conjugate to a new pair of
superfields. In terms of these new superfields the N=4 Lagrangian takes a
(non-polynomial) manifestly MHV form, containing vertices involving two
superfields of negative helicity and an arbitrary number of superfields of
positive helicity. We also discuss constraints satisfied by the new
superfields, which ensure that they describe the correct degrees of freedom in
the N=4 supermultiplet. We test our derivation by showing that an expansion of
our superspace Lagrangian in component fields reproduces the correct gluon MHV
vertices.
