The talk will be held at the AXA Equitable Center in Manhattan at 10 a.m. ET on Tuesday.
"We have hundreds of hours of internal video, Ackman told CNBC's Halftime Report. "We have some internal documents that were given to us by some employees."
"This will be the most important presentation that I have made in my career," he said. "We won't disappoint."
The hedge fund manager also invited Herbalife CEO Michael Johnson to attend the talk and "sit in the front row."
"The company is clearly panicking," Ackman said of Herbalife's recent Twitter campaign that called him the "Worst of Wall Street."
"These so-called nutritional clubs—places where people get together to talk about losing weight—that's not what's happening at these venues," he said.
Herbalife stock was down more than 6 percent after the interview.
"Herbalife is a company about great products and great company," said CFO John DeSimone in a statement. "We are proud of the tireless efforts of our millions of members around the world and know that their passion is what makes Herbalife the incredible company it is today."
DeSimone will be on CNBC at 9 a.m. ET on Tuesday.