Abstract: A pet seat system, apparatus, and method for attaching to a chair. A pet sidecar apparatus is disclosed that includes a basket, a platform configured to support the basket, and one or more straps configured to attach the pet sidecar apparatus to the side of a chair. The pet sidecar apparatus provides a comfortable area for a pet to sit while at the level of the human user. The pet sidecar apparatus moves with a rollable desk chair and does not impede the motion of the desk chair while the human user is able to sit in the desk chair. The pet sidecar apparatus has an easily cleanable universal design that can fit a variety of desk chairs and is safe for both the pet and the human user.