The canonical structure of supergravity with a cosmological constant is analyzed in 2 + 1 dimensions using the Dirac constraint formalism. Using the approach of Henneaux, Teitelboim and Zanelli, the first class constraints are used to find the local gauge symmetries of this model. Provided the cosmological constant is negative, this novel gauge algebra closes, without having to invoke the equations of motion or introducing auxiliary fields. There are two Bosonic and one Fermionic gauge symmetries.