The 25-year-old tv star was walking home from the gym in Sydney's Surry Hills when he noticed a suspicious-looking man stalking a young woman.
"He just made a run for her. He ran 10 or 15 minutes and grabbed her full around the body and threw her to the ground," he told The Daily Telegraph.
Orpheus also told the publication he "instantly" had a bad feeling when he saw the man on Waterloo Street in Sydney's inner-city.
The young actor, who plays a student doctor on Home and Away, said he felt so uneasy about the man he felt compelled to follow him for a couple of blocks.
"My gut told me something was up. I was pretty frightened but the adrenaline kicked in. My initial reaction was for me to step in and to help," he said.
Orpheus appeared on Sunrise on Friday and said, "I was screaming and yelling saying 'stop stop stop', I made sure he got off her."
"There was a split decision, there was a moment where I thought 'wow, this is actually happening' so of course I had the choice, but the way I was brought up I just did what I thought was right," he added.
"I didn't think of the consequences in the moment. I just needed to do what I could to help."
Reflecting on his witness testimony in court earlier this year, he recalled: "He was trying to run away, but I had a hold of this guy telling him 'you're not going anywhere'."