This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$ proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of $35\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$. No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. Within this framework, for ${A}_{0}=0\text{ }\text{ }\mathrm{GeV}$, $\mathrm{tan}\ensuremath{\beta}=3$, and $\ensuremath{\mu}>0$ and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.