He was only able to slip on the striped blazer and waistcoat for a brief dabble with Deco before boarding a flight later last night.
"It's been frantic, I would have liked to stay," Mr Key said.
Overlooking a panoramic vista of Napier from The Dome, the Prime Minister offered his appreciation for the event which brought the city to life.
"It's a great celebration of culture and heritage and of course the '31 earthquake, the big thing is it's a good way of showcasing New Zealand and the Bay to people from all around the world," he said.
Below the sun was setting on devotees of the popular weekend, who gathered for a Public Opening Ceremony at the Sound Shell followed by the hum of planes above during flying displays and a Big Sounds Tonight concert.
This was his third time Mr Key had been in town to witness the roaring 20s glitz and glamour - each time the weather had been more spectacular than the last.
"It's sensational, it's always great when I come to Hawke's Bay, but this time it has managed to exceed itself."
Art Deco Trust general manager Sally Jackson said this year was set to be a bigger every way, with increased overseas interest showing the event was still growing.
"Everybody seems to be having fun, it's good to see everyone dressed up it just gets better and better... We have got about 15 international media and probably about the same number of domestic.
"It's the response of about 18 months promoting Hawke's Bay with the hook as Art Deco Weekend we have noticed the international numbers are up."
They hoped to expand in future years.