He's been practicing for weeks.
Although nine Republicans will take part in the forum, which begins at 4 p.m. EDT in Dearborn, Mich., the focus will be on Thompson, a former Tennessee senator.
A late entry into the race, Thompson has sometimes struggled to answer questions on the campaign trail in his initial weeks as a full-fledged candidate.
He's no stranger to the small screen. He spent years acting on NBC's "Law & Order." But the last time he engaged in a political debate was 1996 during his successful Senate re-election campaign.
Over the past two weeks, Thompson has held seven to nine debate sessions at his McLean, Va., campaign headquarters outside Washington, aides say. In each session, Thompson would answer timed questions on a variety of subjects. Aides then would stop and review answers with him.
Among those helping: former New York Sen. Alfonse D'Amato, who has played Rudy Giuliani.
"We think that we'll hold our own, but obviously every other candidate on the stage has been going to these debates all year long. They've already gone through their preseason. This is our first scrimmage," said Todd Harris, a Thompson spokesman. "The most important thing for us is for Fred's message and answers to connect with Republican voters, and that's been our focus."
During the two-hour Michigan debate, Thompson will be positioned between top GOP rivals Giuliani and Mitt Romney. The debate is sponsored by The Wall Street Journal, CNBC and MSNBC and will focus on economic issues.
Thompson entered the campaign on the same day as the fifth GOP debate last month. He chose to announce his candidacy on NBC's "The Tonight Show with Jay Leno" in Los Angeles instead of debating in New Hampshire, a decision that drew attention.