A dog who has waited almost six years to be adopted has finally found a forever home thanks to a giant billboard and lengthy social media campaign.

Six-year-old Merrick has waited in a shelter in Kansas for most of his life for a family to adopt him, according to The Guardian.

Despite an expensive campaign funded by a benefactor including a dozen different photoshoots and more than 100 online videos Merrick still hadn’t found a happy home.

That was until his new owner Jordan Nussbaum came to the rescue after seeing a billboard featuring the dog's portrait appealing for someone to adopt him.

After seeing the advert, a $3,000 investment as part of the quest to help Merrick get adopted, Mr Nussbaum decided to give the dog the home he deserved.

"I saw the billboard and from that point on I told my girlfriend about him," Mr Nussbaum told Kansas City TV station KMBC.

"It breaks my heart that he sat there, but I think that it was destined that he wait there that long until I was ready for another dog.

"It was love at first sight. What they wanted was someone without kids who had a lot of energy to keep up with him because he’s a large dog. But he's still a puppy. I just seem like I was destined to be with him."

The dog had spent five and a half years at Humane Society of Greater Kansas City.

His benefactor, Scott Poore, is the owner of Mission Driven, a Kansas-based clothing company that donates money to support shelters for homeless pets.

“It’s unbelievable it was this hard of a process," Mr Poore said.

"We were telling the same story to the same audience for those five and a half years but when Mission Driven bought the billboard we reached a whole new audience.”