Hayne made the announcement on Twitter.
IT ALWAYS WORKS OUT! I thank GOD for WHAT HE has done and going to do on this incredible journey!! I'm on the 53 MAN ROSTER FOR THE #49ers.— jarryd hayne (@jarrydhayne_1) September 5, 2015
On a conference call later Saturday, Hayne said the last 10 minutes before he received a congratulatory text from coach Jim Tomsula were the most nerve-racking.
"What's going on?" Hayne recalled thinking. "Do I get a phone call? Is someone going to tell me I've got a job, or what?
"That was probably the first time I've been nervous in a while."
Hayne said he was on the San Francisco waterfront, about 45 miles north of Levi's Stadium, with family when he got the message.
Tomsula, meanwhile, said in the conference call that his text to Hayne read, "You've got yourself to the starting line, and it's a long race."
Hayne might be on the roster because of his performance in Week 2 of the preseason -- he rushed for 54 yards on eight carries and returned three punts for 84 yards against the Dallas Cowboys. He helped solidify his spot in the preseason finale, with 58 yards rushing on 10 attempts, two receptions for 17 yards and three punt returns for 43 yards while also running over a hapless San Diego Chargers cornerback on a catch-and-run.
Hayne's preseason total of 175 rushing yards on 25 carries was second in the NFL, behind the Detroit Lions' Zach Zenner. His 7.0 yards per carry led the league, and his 163 yards on 10 punt returns ranked third.
"It's been really fun to watch. Right off the bat you notice how well he can catch a ball," veteran place-kicker Phil Dawson said. "Catching a punt is probably one of the toughest skills in the NFL, and he's just stepped right in and looks like a natural."
Australian media highlighted Hayne making the roster early Sunday, Australia time.
"Hayne Plane arrives on schedule," The Australian newspaper said.
The Sydney Morning Herald said Hayne "completed one of the greatest code-switches in sporting history."
"I don't think words really describe how great it is to see so many people support me, all the Aussies," Hayne said during the conference call. "Australia is such a sporting country that we're very proud of where we're from. To see so many people get behind me and everyone over here in America obviously just having fun and chasing dreams, I can't begin to thank them. And I thank everyone back home for their love of sport."
His next step? Reporting to the team facility in Santa Clara, California, on Monday and, as he said, "Start getting paid some real money, which is, you know, pretty good."
Hayne signed with the Niners over the Detroit Lions for $100,000.
"This whole journey was never about making a roster or being on a team; it was all about giving myself an opportunity," he said. "It was about saying that I want to take a risk, I want to put myself out there. I want to let my faith be in action.
"Faith without action is dead. This whole journey, I've never felt so alive."
Australian Broadcasting Corporation radio said Hayne had gone from "curiosity to star" in a matter of weeks in the United States.
"It's a great day in San Fran," Hayne said. "The sun's out and there's no clouds in the sky, so it's been a great day."
Probably even brighter in Australia now.
The Associated Press contributed to this report.