The species was first described scientifically by mycologists Karl Vernes, Melissa Danks, and Teresa Lebel in a 2010 issue of the journal Persoonia.

[1] Cortinarius sinapivelus has sequestrate fruit bodies, so its spores are not forcibly discharged from the basidia, and it remains enclosed during all stages of development.

The internal spore-bearing tissue of the cap (the hymenophore) is pale cinnamon brown at first, but darkens later as the spores mature.

The thin-walled basidia (spore-bearing cells) are hyaline (translucent), club-shaped to cylindrical, four-spored, and have dimensions of 26–29 by 7–8 μm.

The fruit bodies were found in the ground under litterfall on the Kaputar Plateau in subalpine grassy woodland.