Catalyzes the first and rate-limiting reaction of the four reactions that constitute the long-chain fatty acids elongation cycle. This endoplasmic reticulum-bound enzymatic process allows the addition of 2 carbons to the chain of long- and very long-chain fatty acids (VLCFAs) per cycle. Condensing enzyme that catalyzes the synthesis of very long chain saturated (VLC-SFA) and polyunsaturated (PUFA) fatty acids that are involved in multiple biological processes as precursors of membrane lipids and lipid mediators. May play a critical role in early brain and skin development. {ECO:0000255|HAMAP-Rule:MF_03204, ECO:0000269|PubMed:20937905, ECO:0000269|PubMed:23479632}. This is the function of ENSG00000118402 (ELOVL4, ELOVL fatty acid elongase 4).