The 29-year-old school teacher said she will be running a gruelling 42 kilometres to raise funds for Cancer Council NSW and help make a difference for Australians affected by cancer.

"While a little apprehensive about the distance, I have done a couple of half-marathons in training and I won't be out to break any records - I just want to finish in memory of dad," Markezic said.

The Sydney Running Festival will mark three months since Jess and her family lost Zoran, widely known as 'Big Z'.

"Dad started coughing before Christmas of 2012," she said. "His cough got increasingly worse so he went and saw our family doctor who sent him for scans in January 2013."

The scans confirmed their worst fears - Zoran had lung cancer.

Zoran endured chemotherapy and radiation, which left him increasingly tired and with a loss of appetite.

Markezic said the support of their extended family, friends and hospital staff was crucial at a time which was testing for the whole family.

"We had 18 relatively good months with him from the time of his diagnosis to his passing.

"I believe we were all as prepared as you can be for these things."

Markezic, along with her two sisters and mum, said his death in June had been hard on her extremely close family.

"He was a fantastic dad who supported us all in everything we did. I was similar to dad in a lot of ways and I constantly strived to be my best so that I could make him proud."

Markezic said it is this reason, along with a bucket-list desire to run a marathon, that has resulted in her training in Kiama for the past eight weeks with a group of people at Life Fit.

"I decided to run the Sydney marathon this year because after dad passed away it felt good to run. I then decided to run for the Cancer Council because I do believe that we only got to have that special time with my dad after his diagnosis because research and medicine have come great lengths in fighting against the disease and its symptoms.

"Mentally, I am ready to run and physically, I have been getting in my set kilometres each week."

To date, Markezic has raised more than $2000, which is well past her initial goal of $1200.

"I think I'm generating support because people think I'm crazy running 42 kilometres," she laughed.

Markezic is encouraging all to join in the fun of the Blackmores Sydney Running Festival on Sunday, September 21.

"I hope that my small contribution will make even a small step towards a world without cancer."

To donate to Markezic and for more about the festival visit http://bsrf2014.gofundraise.com.au/page/JessicaMarkezic.