David Maguire will tackle the City2Surf on August 10, along with grandsons Jack Byrnes and Liam Bowles.
They are raising money for the Bears of Hope charity organisation, which provides support for families who have lost a baby.
READ MORE: Click here to read our previous coverage on Bears of Hope.
Mr Maguire, 67, of Bella Vista, whose daughter Amanda Bowles founded the charity, said he was happy to participate this year.
"It's always been an ambition of mine, but circumstances didn't allow it," Mr Maguire said.
"It's a good cause: a way to contribute and a good way to take part in an iconic event."
While Mr Maguire is thrilled to compete this year, it may not have happened due to health complications.
"I was a bit concerned I wouldn't be able to do it, as I had to have surgery for a tumour on my vocal cords, but we still managed to do it," he said.
Cousins Jack Byrnes, 14, and Liam Bowles, 11, are looking forward to the event.
"Every Saturday I'm part of the Active Walking Group and we do running, sprinting, walking and mini challenges such as squatting or one time we saw a set of stairs and we had to run up and down three times" Jack said.
"I've done a couple of fun runs before, so I'm quite excited about it."
The trio are now training together for the event, recently doing an eight-kilometre walk.
Mr Maguire also hopes that by participating he is promoting the values of Bears of Hope.
"We'd hope that we can get the message out, there is hope available . . . and there is help available to a family after a loss" he said.
To donate search for Bears of Hope at http://fundraise.city2surf.com.au.