Jessica Simpson -- Professional Fat Person

Jessica Simpson is now getting paid for being fat -- the singer just announced ... she's the newest spokesperson for Weight Watchers.

Jessica made the announcement moments ago on her Twitter, writing, "So excited to be a part of the @WeightWatchers family!'

Jess don't come cheap neither -- the Weight Watchers deal is reportedly worth $4 MILLION.

The singer reportedly gained 65-75 POUNDS during her recent pregnancy -- and Weight Watchers must be waiting for a big reveal ... because Jessica hasn't been photographed in public since she gave birth.

WW also released a statement, saying, "We’re thrilled that Jessica Simpson has chosen to join Weight Watchers to adopt a healthier lifestyle and inspire others to do the same."