Summary: In this article, we address the Cauchy problem for the KP-I equation \[ \partial_t u + \partial_x^3 u - \partial_x^{- 1} \partial_y^2 u + u \partial_x u = 0 \] for functions periodic in \(y\). We prove global well-posedness of this problem for any data in the energy space \(\mathbf{E} = \big\{u \in L^2(\mathbb R \times \mathbb T)\), \(\partial_x u \in L^2(\mathbb R \times \mathbb T)\), \(\partial_x^{- 1} \partial_y u \in L^2(\mathbb R \times \mathbb T) \big \}\). We then prove that the KdV line soliton, seen as a special solution of KP-I equation, is orbitally stable under this flow, as long as its speed is small enough.