Harrison, 47, told People.com he and Burditt plan to swap vows July 21 at the Ritz Carlton in Southern California's Laguna Beach.
"It will be a lot of friends and family," Harrison told the magazine. "It started off with about 40 people and it's well over 100 people now. You know how those things go."
The prospective groom also said Danny Koker of the History Channel's "Counting Cars" will become an ordained minister and officiate the wedding, while Harrison's "Pawn Stars" co-star Chumlee Russell is to be the ring bearer.
"I can't make that up," he said. "I just had no idea there was so much involved. I just thought you got a cake, had a party, buy a keg. But we're getting it done."