Summary: We show that string duality relates M-theory on a local Calabi-Yau fourfold singularity \(X_{4}\) to type IIA string theory on a Calabi-Yau threefold \(X_{3}\) fibered over a real line, with RR 2-form fluxes turned on. The RR flux encodes how the M-theory circle is fibered over the IIA geometry. The theories on \(N\) D2 branes probing \(X_{3}\) are the well-known quiver theories with \({\mathcal N}=2\) supersymmetry in three dimensions. We show that turning on fluxes, and fibering the \(X_{3}\) over a direction transverse to the branes, corresponds to turning on \({\mathcal N}=2\) Chern-Simons couplings. String duality implies that, in the strong coupling limit, the \(N\) D2 branes on \(X_{3}\) in this background become \(N\) M2 branes on \(X_{4}\). This provides a string theory derivation for the recently conjectured description of the M2 brane theories on Calabi-Yau fourfolds in terms of \({\mathcal N}=2\) quiver Chern-Simons theories. We also provide a new \({\mathcal N}=2\) Chern-Simons theory dual to \(AdS_{4}\times Q^{1,1,1}\). Type IIA/M-theory duality also relates IIA string theory on \(X_{3}\) with only the RR fluxes turned on, to M-theory on a \(G_{2}\) holonomy manifold. We show that this implies that the \(N\) M2 branes probing the \(G_{2}\) manifold are described by the quiver Chern-Simons theory originating from the D2 branes probing \(X_{3}\), except that now Chern-Simons terms preserve only \({\mathcal N}=1\) supersymmetry in three dimensions.