Mark Woods has had Walnut since he was a puppy.
Now 18 years old and "on his last legs", the dog is going to be put down on Saturday morning.
But before his best friend's death, Mark wants to take him for a stroll on a beach in Cornwall and he wants company.
Mr Woods who lives in Newquay said he is "flabbergasted" by the response to his social media appeal for people to join him on Walnut's last walk.
More on Walnut's last walk, plus more Devon and Cornwall news.
He said: "Sadly I am having to have Walnut euthanised on Saturday and so we will be having a last walk together on his beloved Porth Beach.
"I would love it if dog lovers or owners and friends would join us for a celebration of Walnut."
He said the reaction has been "incredible" with people from as far afield as Surrey and Derbyshire offering their support.
The event is being shared on social media under #walkwithwalnut.
Mr Woods has three other whippets but said Walnut "has got something about him" and they've been through an "awful lot together".
That includes two marriages, three engagements and a move from London to Cornwall.
He is taking Thursday and Friday off work so he can spend time with his much loved pet and give him the best possible send off.
According to his owner, Porth Beach, which is closed to dogs during the summer months, is Walnut's favourite beach.
A dog owner is appealing for people to join him on his last walk with his beloved whippet.