Wood White, a cloudy Belgian white beer, was named after a butterfly species that has declined by 88% since the 1970s.
More than 300 pubs will stock the limited-edition drink, including the Strangers' Bar in the Palace of Westminster.
Sales will go towards funding future conservation work for the butterfly across the West Midlands region (£10 per cask).
Wood’s Brewery worked with wildlife charity Butterfly Conservation (BC) on the 4.2% ABV brew, which will be available until early June.
Brewery co-owner Stephen O’Neill said: “We are proud to be part of such an important local conservation project. Supporting the Wood White butterfly with a white ale from Wood’s Brewery couldn’t be a better fit. Preserving our region’s environment and working with our local community is integral to what we stand for.
“The Wood White is a classic Belgian style hazy white with subtle coriander aromas, and crisp orange peel and citrus flavours. It will be perfect for savouring on long spring and summer evenings.
“A white, cloudy beer is a rarity in the cask world, but we’re aiming to release it in bottle form too at a later date. As it is unfined, it is suitable for vegetarians and vegans. We hope drinkers will find the beer’s unusual style memorable and will join us in raising funds for this special local butterfly.”
The beer will be available from Wood’s Brewery in cask format from tomorrow (Wednesday 24 April).