The Standard Model of particle physics provides a remarkably predictive and well-tested theory for describing the interactions of the known elementary particles. However, the observed matter/antimatter asymmetry, the existence of small neutrino masses, and cosmological constraints on dark matter and dark energy point strongly to the existence of fundamental physics beyond the Standard Model. In the past few decades, ultra-low-background liquid xenon time projection chambers (TPCs) have emerged as a powerful experimental technique in the search for low energy signatures of new physics. This talk will describe their application in two different areas: searches for neutrinoless double beta decay (focusing on the nEXO experiment) and direct searches for dark matter. I will discuss the sensitivity of the upcoming generation of experiments, as well as ongoing work to maximize their physics potential and extend their scientific impact in new directions.