Mammalian SWI/SNF chromatin remodeling complexes exist in three distinct, final-form assemblies: canonical BAF (cBAF), PBAF, and a newly characterized non-canonical complex, ncBAF. However, their complex-specific targeting on chromatin, functions and roles in disease remain largely unknown. Here, we comprehensively map complex assemblies on chromatin and find that ncBAF uniquely localizes to CTCF sites and promoters. We identified ncBAF subunits as major synthetic lethalities specific to human synovial sarcoma and malignant rhabdoid tumor, which share in common cBAF complex perturbation. Chemical and biological depletion of the BRD9 subunit of ncBAF rapidly attenuates SS and MRT cell proliferation. Notably, in cBAF-perturbed cancers, ncBAF complexes retain localization to CTCF sites and promoters, and maintain gene expression at retained mSWI/SNF sites to support cell proliferation in a manner distinct from fusion oncoprotein-mediated targeting. Taken together, these findings unmask the unique targeting and function of ncBAF complexes and present new cancer-specific therapeutic targets.