Hayne, who recently turned 27, is a former MVP of the National Rugby League who quit the sport in October to pursue a NFL career. He was believed to be expected to sign a futures contract with the Detroit Lions, however the Sydney Morning Herald reports the "lifestyle" of San Francisco as compared to Detroit factored into his decision to choose the 49ers.
On Monday, Hayne sent out a tweet saying "Today a dream becomes a reality. With God anything is POSSIBLE."
In October, former Lions running back Reggie Bush said he believed Hayne has the skills to play in the NFL.
"I just think he's a good athlete," Bush said, according to the Detroit Free Press. "I've seen some of his film, I watched him and he has all the skill sets that it takes to play in the NFL. He's a great athlete and I told him I definitely think he has a future in the NFL if he's serious about it."
According to the Morning Herald, Hayne recorded 4.53 seconds in the 40-yard dash at his pro day in December.
Futures contracts can be signed as soon as the previous regular season has concluded and count only against a team's 90-man training camp roster limit for the following season. Any player not on an NFL active roster when the previous regular season ended is eligible to sign a futures contract.