Saracens back row Sean Reffell will join Ulster next summer, while John Cooney and Will Addison have signed contract extension.
The Ireland-qualified Reffell was Sarries Young Player of the Year in the 2020/21 season.
A former England U20 international, openside Reffell has made almost 40 appearances for Mark McCall's side since making his debut in 2017.
He also holds the Saracens record for most tackles in a game (39) in the Premiership Rugby Cup semi-final versus Worcester in 2019.
"We are looking forward to welcoming Sean to the province next summer," said Dan McFarland.
"With an already impressive track-record for Saracens, he will be a great fit alongside some real quality in our back row, and I am confident he will be a valuable addition to our squad."
Meanwhile, Ireland internationals Cooney and Addison have committed their futures to the club, although the length of their new deals was not disclosed.
Since joining Ulster in 2017, 31-year-old Cooney has been a key player and the scrum-half's performances for the province have seen him consistently rank among the top points-scorers in the United Rugby Championship, competition.
Utility back Addison, who is currently out injured, is set to continue in the Ulster set-up. The 29-year-old, who is equally comfortable in midfield and at fullback, has been with the province since 2018 after racking-up over 100 appearances for Sale Sharks.
McFarland added: "John is a valued member of our squad, who continues to play a central role in the team, both on and off the field.
"It is great that he has bought into our ambitions for the future, and his experience and skills will play an important role in helping us to achieve those.
"I am also delighted that Will is remaining with us, and I look forward to seeing him back out on the field soon.
"Will has been extremely unlucky with injury recently, but with his play-making abilities and versatility, he is set to continue to make an impact for Ulster in the time ahead."
Earlier it was announced that Ulster prop Gareth Milasinovich has joined Saracens on a two-month loan deal.
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