The Belle and Belle II experiments have collected a combined sample of $1.2~$ ab$^{-1}$ of collisions at a centre-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. These data, with low particle multiplicity and constrained initial state kinematics, are an ideal environment for studying semileptonic and leptonic decays of the $B$ meson. Combined with theoretical inputs, measurements of both inclusive and exclusive semileptonic decays yield information about the Cabibbo-Kobayashi-Maskawa matrix elements $|V_{cb}|$ and $|V_{ub}|$. Our latest results based on the Belle II data set are reviewed. We also present the first measurement of $B^+\to\tau^+\nu_\tau$ from Belle II. This decay provide constraints on beyond-the-standard model physics and provide alternative measurements of $|V_{ub}|$ that complement those from semileptonic decay.