Hastings has played 36 first grade games for the Roosters over the past three years after making his NRL debut in round 26 of the 2014 season.
Head of Football Bob Fulton said the signing of Hastings is a major boost for the club.
“We are delighted to bring in to our club an exciting young player who can cover several key positions and is an excellent goal-kicker,’’ Fulton said.
“At the age of 20, Jackson’s rugby league career is ahead of him and we want him to be at the Sea Eagles long term.
“As a junior, he was without peer and being the son of a great player in Kevin Hastings obviously has placed extra pressure on him. There will be none of that at Manly.
“We consider him to be one of the most outstanding young players in the game and often a change of clubs can bring about the necessary changes needed for Jackson to fulfil the promise he showed throughout his junior career.
“Both Trent Barrett and I consider him to be a real boost to our 2017 squad and we welcome him to our club.”
Sea Eagles Coach Trent Barrett said Hastings was a great signing for the club.
“Jackson is a young player with tremendous talent who can easily play several positions,’’ Barrett said.
“He comes to Manly looking to secure a permanent starting spot and his experience gives us good depth in and around the halves and at hooker.”
Barrett has enjoyed a long association with the Hastings family, starting when they were neighbours in Wollongong.
“I’ve known Jackson his whole life pretty much and he’s an exceptional player,’’ Barrett added.
“We’ve watched him since he was a kid and he’s always been a standout coming through the juniors.”