The trio will be seen partnering forces personnel on the Chris Tarrant-fronted general knowledge quiz. Bonneville will join Royal Navy submarine engineer Lieutenant Gary Beels, Sykes will team up with Army medic Major Nicole McCullough and Thomson will partner Sergeant Derek 'Dutch' Holland from the Royal Air Force.
Bonneville said: "I am absolutely dreading my encounter with the Smiling Tormentor, otherwise known as Chris Tarrant. However, I have every confidence that Lieutenant Beels is a genius.
"I only hope that when he realises I am as thick as two short planks he doesn't make me walk one of them."
> War heroes for 'Millionaire' special
Bonneville added that he is confident the pair will have "a lot of fun" raising funds for The Royal Navy and Royal Marines Charity.
Thomson described the invitation as "a great honour", while Sykes joked that appearing on the show would be "utterly terrifying".
"I'm only hoping that my partner Nicola is as clever as she is brave," she added.
All the money won will be donated to armed forces benevolent charities, in a change from the usual Who Wants to Be a Millionaire? special format where winnings are split with a member of the public.
The Who Wants to Be a Millionaire? Remembrance Special will air on Wednesday, November 9 at 9pm on ITV1.
Watch John Thomson and the cast of The Fast Show talking to Digital Spy below: