We consider the semiclassical magnetic Laplacian L on a Riemannian manifold, with a constant-rank and non-vanishing magnetic field B. Under the localization assumption that B admits a unique and non-degenerate well, we construct three successive Birkhoff normal forms to describe the spectrum of L in the semiclassical limit → 0. We deduce an expansion of all the eigenvalues under a threshold, in powers of 1/2 .