Montgomery's Lemma on the torus T d states that a sum of N Dirac masses cannot be orthogonal to many low-frequency trigonometric functions in a quantified way. We provide an extension to general manifolds that also allows for positive weights: let (M, g) be a smooth compact d−dimensional manifold without boundary, let (φ k ) ∞ k=0 denote the Laplacian eigenfunctions, let {x 1 , . . . , x N } ⊂ M be a set of points and {a 1 , . . . , a N } ⊂ R ≥0 be a sequence of nonnegative weights. ThenThis result is sharp up to the logarithmic factor. Furthermore, we prove a refined spherical version of Montgomery's Lemma, and provide applications to estimates of discrepancy and discrete energies of N points on the sphere S d .