The Bessbrook boy was diagnosed with a serious form of leukemia last summer and requires life-saving treatment.
So far, large-scale treatments have not proven successful.
But on Monday, Bobby's mother Louise confirmed that a donor had been found and made an emotional appeal to those who have followed Bobby's journey.
“I have heard that there is a donor for Bobby and he will be admitted to the hospital tomorrow (Tuesday) to start the process,” she wrote on social media.
“He will have to undergo eight days of aggressive chemotherapy and radiotherapy before undergoing the transplant.
“They told us that they had to choose a donor who was not a perfect match because Bobby needed an urgent match.
“This could mean many side effects on top of those from chemotherapy and radiotherapy.
“We ask everyone to pray that Bobby's side effects are minimized and that he gets through this difficult time.”
This comes just weeks after a 'Swab for Bobby' bike ride and fun day was held at Shane O'Neill's GAA Club in Camlough.
The family wanted to gather as many people as possible in hopes of finding a suitable match.
Dad Danny expressed optimism in a video posted ahead of the event at the end of June.
“I was asked the other day if I would ever find this donor, and I said, 'Yes, I will never give up on finding this donor,'” he said.
“My son Bobby believes that.
“The other day he put his arm around me and whispered in my ear, 'Daddy, we're never going to give up.' We're never going to give up.”
In the latest update, his mother Louise acknowledged that her son “has a tough journey ahead” and appealed for prayers and support.
Newry and Armagh MLA Justin McNulty was among those celebrating the news.
“The Brown family has been in our hearts and minds as they have searched for a match for their young son Bobby, and it would be a huge relief if a match was found that would enable life-saving treatment.” There will be a feeling and a sense of hope, “Bobby,'' he said.
“Bobby’s resilience, along with the determination of his parents Louise and Danny, is a source of inspiration to many people in the local area, and this is evidenced not only by the outpouring of sympathy for the family but also by the huge number of people who These are the people who came forward to be tested in search of someone to marry.”
SDLP representatives said Bobby's story “underscores the importance of registering as a bone marrow donor” and encouraged anyone who has not yet done so to do so.
“It could potentially save someone's life,” McNulty said.
“Your goodwill and goodwill will continue to follow Bobby as he embarks on the next phase of his treatment.
“We wish the Brown family, especially Bobby, the best of luck through his treatment and transplant.”
