The cell wall is a shape-defining and protective structure that envelops virtually all bacteria. Wall-less variants, called L-forms, have been generated in laboratories for many decades under highly specialized conditions, invariably aimed at interrupting cell wall synthesis. As such, the relevance of these cells has remained obscure. Here we show that the filamentous actinomycete Kitasatospora viridifaciens has the natural ability to switch between a wall-less state and the canonical mycelial mode-of-growth. We show that this organism thrives in a cell wall-less form, and identify the polar growth determinant DivIVA as an essential regulator required for reversible metamorphosis. This is the first report of a reversible metamorphosis in a bacterium that includes wall-less cells as a natural stage in bacterial development.