A star in the SANFL, Hayes was only added to the Saints' rookie list two weeks ago after training with the club in December.
The 25-year-old has been overlooked at AFL level for years but will get a chance on the big Friday night stage in round-one.
"This is a great story to get on an AFL list at 25," St Kilda coach Brett Ratten said.
"He's worked extremely hard, probably got knocked back and told he couldn't do certain things but he just kept persisting.
"I'm really pleased he's at our football club, not only for his football ability, but him as a person.
"The players love him and he's fitted in perfectly."
The Saints will also blood teenager Mitch Owens, who was drafted by the club with pick 33 in last year's draft.
A member of St Kilda's next generation academy, the Saints have high hopes for the midfielder.
St Kilda are coming off an inconsistent season following a semi-finals berth in 2020.
The Saints were good enough topple finalists such as the Brisbane Lions, but also suffered some losses.
Ratten is delighted with how St Kilda have attacked the pre-season but suffered crucial injuries to Hunter Clark and Jack Billings in their final practice match.
"We copped a few (injuries) last week, but that's footy, and I think every club whether it's injuries or COVID will be going through some ups and downs with their best 22 on the park this year," Ratten said.
Collingwood will unveil debutants of their own, with father-son star Nick Daicos to run out after being the Magpies' first pick in last year's draft.
The Magpies will be without forward Will Hoskin-Elliott and assistant coaches Brendon Bolton and Josh Fraser, who are all isolating at home due to COVID-19 protocols.
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