"These volunteers provide driving, respite sitting and fundraising services for people with cancer, their friends, families and carers," McCullum said.
"They're always there for us when we need their help, but to ensure that support continues in the future, they need ours now."
New Hawkes Bay Racing chief executive Andrew Castles said it was a day on which the entire racing community united to support the Cancer Society in its fight against the disease.
"The fact that Brendon McCullum has taken time out of his busy schedule to join this fight is an absolute thrill," he said.
McCullum will be hosted by Westbury Stud, the sponsor of the main race and where stallion Mafki stands.
Daffodil Race Day is a fundraiser for the Hawke's Bay Cancer Society and entry to the Hastings racecourse will be by donation.