John Craig had been spearfishing near Shark Bay, around 500 miles (805km) north of Perth, when he became separated from his boat in waters home to the deadly predators.
Screaming for help, the 34-year-old soon realised that his desperate attempts to draw attention to himself had attracted one of the bay's killer residents.
He said in a Facebook post: "I had been splashing and screaming for some time and my heart rate was sky high.
"I put my head in the water to check I was in the same place and suddenly saw a huge 4m (13ft) tiger shark approaching within arm's reach.
"It was easily the biggest tiger shark I've been in the water with and that's saying something, having worked as a dive instructor for over 10 years.
"I quickly turned and saw another large sandbar whaler circling behind me and it was at that point I decided to give up on getting to the boat and save myself."
Mr Craig said watched as the shark circled him before approaching him "multiple times from different angles".
"It was definitely trying to work out what I was and whether I could be 'on the menu', but each time it approached I used my spear gun to block its path.
"At no point did I touch the shark as I didn't want to upset it with a prod from the spear and make a bad situation worse."
After two minutes locked in a "dance" with the shark and fearful of "upsetting" it, Mr Craig realised he had to make a life-or-death attempt to get to shore - although he was unable to shake off the predator.
"At this point I thought I was gone - four nautical miles (4.6 miles) out to sea with a huge tiger shark following me - I thought this was it, this is how I'm going to die," he said.
As he headed for land, which he knew remained a huge swim away, Mr Craig said he was constantly aware of the shark following a short distance behind.
He watched as it would disappear into the gloom "then suddenly reappear behind me, just keeping pace with me behind my fins".
At one point the shark cruised beside him as if it was a whale shark, a harmless cousin of the tiger species.
"For about 500m the shark swam on the same path as me towards the shore and then in a moment banked and disappeared completely as if to say 'You're OK now, I'll leave you alone'," Mr Craig wrote.
However, while out of sight, the shark was not out of Mr Craig's mind - and he still faced a swim of "around three hours" to get back to safety.
"The next part was pure endurance; I had to swim constantly looking around from all angles to make sure there wasn't an unwelcome visitor, with my spear gun pointed behind me to stop anything grabbing my fins," he said.
Exhausted and barely able to stand, he reached the shore in an isolated location and faced having to walk in search of rescue.
"I just thought about my wife and how worried she'd be. I just wanted to tell her I was alive," he said.
Luckily he was spotted from the air and he was picked up by a boat from the Shark Bay Volunteer Marine Rescue.
Despite the harrowing experience that, by his own admission, he was lucky to survive, Mr Craig said he does not want to put people off Shark Bay as a diving and snorkelling destination.
"These animals are apex predators but we are not 'on the menu', he said. We need them in the oceans and as much as it was scary at the time I can only reflect on how beautiful that big female tiger shark was."