Mr McLeod's daughter Tracey McLeod found out about her father's plan on Saturday.
"It's all happened last minute,"she said. "He only rang me on Saturday night, he doesn't do anything by halves."
She helped set up the web page for Mr McLeod, despite her initial shock.
"When you've lost a parent, you worry twice as much about the remaining parent and I didn't want him to overdo it, or risk his own health, but there was no talking him out of it," Ms McLeod said.
Mr McLeod's wife and sister were diagnosed with cancer at similar times in 2010, and died a few months apart this year.
"He's been brave and we admire his strength throughout the ordeals that life has thrown at him, particularly in the last year," said Ms McLeod.
"This is a tribute to both mum and Tilda".
Walking a half marathon was an important way of honouring the active pair.
Alison was a silver and bronze national New Zealand medal winner and Tilda remained fit throughout her life.
Kirstie Cox, Mr McLeod's niece and Tilda's daughter, said that her mother would be thrilled with what Mr McLeod was doing.
"My mum just loved tramping, it was one of her passions. For Doug to do something like this, she would be so proud of him," Ms Cox said.
Spokeswoman for the Waikato/Bay of Plenty division of the Cancer Society Maria Low said Mr McLeod's efforts were an important part of Cancer Society appeals.
"It is wonderful to see so many people of all ages fundraising to support people with cancer."
Mr McLeod said partaking in the Walking Star event would be a good opportunity for his family to meet up for a good cause. "After the year we've had, it'll be great to get together without attending a funeral," he said.
Mr McLeod's had raised $4500 on Friday .