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 with higher activity toward C18 acyl-CoAs, especially C18:3(n-3) acyl-CoAs and C18:3(n-6)-CoAs. Also active toward C20:4-, C18:0-, C18:1-, C18:2- and C16:0-CoAs, and weakly toward C20:0-CoA. Little or no activity toward C22:0-, C24:0-, or C26:0-CoAs. May participate in the production of saturated and polyunsaturated VLCFAs of different chain lengths that are involved in multiple biological processes as precursors of membrane lipids and lipid mediators. a very-long-chain acyl-CoA + H(+) + malonyl-CoA = a very-long-chain 3-oxoacyl-CoA + CO2 + CoA eicosanoyl-CoA + H(+) + malonyl-CoA = 3-oxodocosanoyl-CoA + CO2 + CoA (5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA + H(+) + malonyl-CoA = (7Z,10Z,13Z,16Z)-3-oxodocosatetraenoyl-CoA + CO2 + CoA (6Z,9Z,12Z)-octadecatrienoyl-CoA + H(+) + malonyl-CoA = (8Z,11Z,14Z)-3-oxoeicosatrienoyl-CoA + CO2 + CoA (9Z,12Z)-octadecadienoyl-CoA + H(+) + malonyl-CoA = (11Z,14Z)-3-oxoicosa-11,14-dienoyl-CoA + CO2 + CoA (9Z)-octadecenoyl-CoA + H(+) + malonyl-CoA = (11Z)-3-oxoicosenoyl-CoA + CO2 + CoA H(+) + malonyl-CoA + octadecanoyl-CoA = 3-oxoeicosanoyl-CoA + CO2 + CoA H(+) + hexadecanoyl-CoA + malonyl-CoA = 3-oxooctadecanoyl-CoA + CO2 + CoA (9Z,12Z,15Z)-octadecatrienoyl-CoA + H(+) + malonyl-CoA = (11Z,14Z,17Z)-3-oxoeicosatrienoyl-CoA + CO2 + CoA Lipid metabolism; fatty acid biosynthesis. The C-terminal di-lysine motif may confer endoplasmic reticulum localization. Belongs to the ELO family. ELOVL7 subfamily.