Mr Irwin, 44, died last Monday after he was pierced in the chest by a stingray's barb while filming a documentary on the Great Barrier Reef.
The service will begin at 9am local time at the zoo’s Crocoseum which seats 5,500 people. Those who attend will have to make a donation to Mr Irwin’s conservation fund Wildlife Warriors to gain admission.
His widow, Terri Irwin said in a statement that while larger venues had been suggested, she believed the croc-hunter would have wanted it at Australia Zoo.
"I cannot see how a memorial service would work in any other place other than the Crocoseum which he built here at the zoo and of which he was so proud," Mrs Irwin said.
"I would therefore ask that everyone please bear with me in this wish and help me to make this happen."
In her first public comment since her husband’s death, Mrs Irwin described Steve as her “soul mate”.
She also thanked the community for their "overwhelming outpouring of love, support and prayers".
The croc hunter's close friend and business manager John Stainton said Mrs Irwin, Steve's father Bob and eight-year-old daughter Bindi would all speak at the memorial service.
Country singer John Williamson, one of Steve Irwin's favourite Australian performers, will play at the service.
The service will be shown on large television screens set up in Brisbane and the Sunshine Coast and will be broadcast live on television in Australia, the United States and Asia.