A chair mountable desk apparatus includes a clamp is removably positioned on an armrest. A first panel has a top side, a bottom side and a perimeter edge. The first panel is mechanically coupled to the clamp and a computer mouse is positionable on the top side. The first panel has a first lateral edge, a second lateral edge, a first end edge and a second end edge. A second panel has an upper surface, a lower surface, and a peripheral edge. A rod is attached to the lower surface and extends outwardly from the peripheral edge. A sleeve is attached to the bottom side of the first panel nearer to the first end edge than the second end edge. A keyboard is positionable on the upper surface. The sleeve receives the rod to position the second panel adjacent to the second lateral edge.