If $\sf PA+\lnot \rm Con\sf (PA)$ is inconsistent but $\sf PA$ is consistent, then in every model of $\sf PA$ it is true that $\rm Con\sf (PA)$, now by completeness we get that Peano proves its own consistency.
If $\sf PA+\lnot \rm Con\sf (PA)$ is inconsistent but $\sf PA$ is consistent, then in every model of $\sf PA$ it is true that $\rm Con\sf (PA)$, now by completeness we get that Peano proves its own consistency.