Cheng "Charlie" Saephan, 46, of Portland, told a news conference held by the Oregon Lottery on Monday that he and his 37-year-old wife, Duanpen, would split the prize evenly with a friend.
Laiza Chao, 55, of the Portland suburb of Milwaukie, had chipped in to buy a batch of tickets with them.
"I will be able to provide for my family and my health," Saephan said, adding that he'd "find a good doctor for myself".
He said as a cancer patient, he wondered, "how am I going to have time to spend all of this money? How long will I live?"
Saephan was born in Laos and moved to Thailand in 1987, before immigrating to the US in 1994.
He wore a sash at the news conference identifying himself as Iu Mien, a southeast Asian ethnic group with roots in southern China.
Many Iu Mein were subsistence farmers and assisted American forces during the Vietnam war.
After the conflict, thousands of Iu Mien families fled to Thailand to avoid retribution and eventually settled in the US, especially along the west coast.
Saephan graduated from high school in 1996 and has lived in Portland for 30 years. He worked as a machinist for an aerospace company.
In the weeks leading up to the drawing, he wrote out numbers for the game on a piece of paper and slept with it under his pillow, he said.
The winning Powerball ticket was sold in early April at a Plaid Pantry convenience store in Portland, ending a winless streak that had stretched more than three months.
The Oregon Lottery said it had to go through a security and vetting process before announcing the identity of the person who came forward to claim the prize.
Under Oregon law, with few exceptions, lottery players cannot remain anonymous. Winners have a year to claim the top prize.
The $US1.3 billion ($A2.0 billion) prize is the fourth largest Powerball jackpot in history, and the eighth largest among US jackpot games, according to the Oregon Lottery.
The biggest US lottery jackpot won was $US2.04 billion ($A3.11 billion) in California in 2022.
