A pet platform assembly configured to securely mount to a window sill may include a base configured to support the weight of a pet, at least one clamp secured to the base, and a support bracket secured to an underside of the base. The clamp is configured to securely mount the base to an edge of the window sill. The support bracket is configured to brace the base with respect to a wall that supports the window sill. The support bracket may include a cord passage that routes the electrical cord therethrough.