Antiporter that transports nucleotide sugars across the endoplasmic reticulum (ER) membrane in exchange for either their cognate nucleoside monophosphate or another nucleotide sugar (PubMed:16965264, PubMed:17599910, PubMed:31423530). Transports various UDP-sugars including UDP-N-acetyl-alpha-D-glucosamine (UDP-GlcNAc), UDP-N-acetyl-alpha-D-galactosamine (UDP-GalNAc) and UDP-alpha-D- glucuronate (UDP-GlcA), which are used by ER glucosyltransferases as sugar donors for the synthesis of sugar chains of glycoproteins, glycolipids and oligosaccharides (PubMed:11322953, PubMed:16965264, PubMed:17599910, PubMed:17952091, PubMed:31423530). May couple UDP- GlcNAc or UDP-GalNAc efflux to UDP-GlcA influx into the ER lumen that in turn stimulates glucuronidation and subsequent excretion of endobiotics and xenobiotics (PubMed:16965264, PubMed:17599910). Plays a role in chondroitin sulfate biosynthesis, which is important for formation of cartilage extracellular matrix and normal skeletal development (By similarity). {ECO:0000250|UniProtKB:A2AKQ0, ECO:0000269|PubMed:11322953, ECO:0000269|PubMed:16965264, ECO:0000269|PubMed:17599910, ECO:0000269|PubMed:17952091, ECO:0000269|PubMed:31423530}. This is the function of ENSG00000116704 (SLC35D1, solute carrier family 35 member D1).