  We consider three dimensional Einstein gravity non-minimally coupled to a
real scalar field with a self-interacting scalar potential and present the
exact black hole formation in three dimensions. Firstly we obtain an exact
time-dependent spherically symmetric solution describing the gravitational
collapse to a scalar black hole at the infinite time, i.e. in the static limit.
The solution can only be asymptotically AdS because of the No-Go theorem in
three dimensions which is resulted from the existence of a smooth black hole
horizon. Then we analyze their geometric properties and properties of the time
evolution. We also get the exact time-dependent solution in the minimal
coupling model after taking a conformal transformation.
