Abstract: The present technology generally relates to animal restraint systems with cinching mechanisms and associated devices and methods. A restraint system, such as a harness for a dog, in accordance with the present technology can include a back strap, a sternum strap, a chest strap assembly, and a cinching mechanism coupled to the chest strap assembly. When an animal or person pulls on a free-end portion of a cinching strap, the cinching mechanism draws opposing sides of the chest strap assembly closer together and, thereby, tightens the harness across the chest of the animal. Cinching mechanisms in accordance with the present technology avoid substantial shifting or rotation of the harness on the neck or torso of the animal in response to a lunging, pulling, tugging, or other force.