Cohesin is a multiprotein ring complex that regulates 3D genome organization, sister chromatid cohesion, gene expression, and DNA repair. Cohesin is known to be ubiquitinated, though the mechanism, regulation, and effects of cohesin ubiquitination remain poorly defined. We previously used gene editing to introduce a dual epitope tag into the endogenous allele of each of 11 known components of cohesin in human HCT116 cells. Here we report that mass spectrometry analysis of dual affinity purifications identified the USP13 deubiquitinase as a novel cohesin-interacting protein. Subsequent IP/Westerns confirmed the endogenous interaction in HCT116, 293T, HeLa, and RPE-hTERT cells; demonstrated that the interaction occurs specifically in the soluble nuclear fraction (not in the chromatin); requires the ubiquitin binding domains (UBA1/2) of USP13; and occurs preferentially during DNA replication. Reciprocal dual affinity purification of endogenous USP13 followed by mass spectrometry demonstrated that cohesin is its primary interactor in the nucleus. Ectopic expression and CRISPR knockout of USP13 showed that USP13 is paradoxically required for both de-ubiquitination and ubiquitination of cohesin subunits in human cells. While USP13 was dispensable for sister chromatid cohesion in HCT116 and HeLa cells, it was required for the dissociation of cohesin from chromatin as cells transit through mitosis. Together these results identify USP13 as a new cohesin-interacting protein that regulates the ubiquitination of cohesin and its cell cycle regulated interaction with chromatin.