  We present the supersymmetric extension of the recently constructed
E$_{8(8)}$ exceptional field theory -- the manifestly U-duality covariant
formulation of the untruncated ten- and eleven-dimensional supergravities. This
theory is formulated on a (3+248) dimensional spacetime (modulo section
constraint) in which the extended coordinates transform in the adjoint
representation of E$_{8(8)}$. All bosonic fields are E$_{8(8)}$ tensors and
transform under internal generalized diffeomorphisms. The fermions are tensors
under the generalized Lorentz group SO(1,2)$\times$SO(16), where SO(16) is the
maximal compact subgroup of E$_{8(8)}$. Vanishing generalized torsion
determines the corresponding spin connections to the extent they are required
to formulate the field equations and supersymmetry transformation laws. We
determine the supersymmetry transformations for all bosonic and fermionic
fields such that they consistently close into generalized diffeomorphisms. In
particular, the covariantly constrained gauge vectors of E$_{8(8)}$ exceptional
field theory combine with the standard supergravity fields into a single
supermultiplet. We give the complete extended Lagrangian and show its
invariance under supersymmetry. Upon solution of the section constraint the
theory reduces to full D=11 or type IIB supergravity.
