Prize Island will see four couples battling it out in an exotic setting in order to win £50,000.
The contestants will be tested on their own relationships, while having to prove their skills in a series of tasks.
The couples will take part in four rounds of challenges, before making their way to the final stage 'Buried Treasure', which contains a new car with the prize money locked inside.
Armstrong said of the show: "Prize Island is inventive, funny, compelling, oh, and set on a tropical island with prizes!"
Willis added: "I am beyond excited to be one of the presenters of Prize Island. It promises to be a show like no other where contestants win unbelievable prizes."
Prize Island is scheduled to air in 2013 on ITV1.
Pointless presenter Armstrong revealed earlier this year that he turned down the chance to host Countdown.