The Rose & Crown in Hay-on-Wye, mid Wales, highlighted the deal on its social media.
Wales Online reported that diners have to eat the entire huge dish in under 25 minutes or they will be charged the full £14.50 price.
The dish includes meat (usually beef, lamb or pork), stuffing, potatoes, vegetables and Yorkshire puddings, and a jug of gravy.
Pub owner Tyrone Metcalfe told the local paper: "It's good, everyone is loving it. The Facebook page is going completely mental.
"We are going to keep this going for about four or five weeks and then change it for some more variety so it doesn't get boring."
The pub shared diners attempting the challenge on its Facebook page.
One diner completed the challenge earlier this week (21 May)
This isn't the only 'challenge' dish the pub offers, as diners can enjoy a 'big breakfast'. This includes six slices of black pudding, eight hash browns, eight rashers of bacon, eight sausages, eight eggs, mushrooms, tomatoes, toast, and a huge portion of baked beans.
The Friday Breakfast Challenge runs from 9.30am until 3pm on Fridays and is £12.
This challenge has been shared more than 2,800 times on Facebook.
The pub also announced a new challenge on its Facebook page of a massive pizza for one and diners have just 25 minutes to complete it.
The Rose & Crown also offers diners the chance to eat its burger stack challenge.