An NBC spokesperson confirmed that the singer, actress and fashion designer is to appear on the March 13 episode of the weight loss show.
Simpson - who is pregnant with her first child - will be promoting her clothing, skincare and handbag lines, giving two challenge winners a tour of her showroom and free gifts.
She said in a statement: "I was so happy when I was asked to help style two contestants from The Biggest Loser. I am truly inspired by how hard these contestants worked to accomplish their goals for a healthy lifestyle.
"It was so much fun seeing them try on clothes they would have never fit into before and feeling sexy. We had an amazing day together!"
Immediately after her stint on The Biggest Loser airs next month, the network will screen the first episode of her new show with fellow designers Nicole Richie and John Varvatos, titled Fashion Star.
Reports which surfaced last year about the star becoming an ambassador for the Weight Watchers brand following her pregnancy were later quashed.
Watch a sneak peek of Jessica Simpson's new show Fashion Star below: