The 32-year-old right-arm seamer will join the club from Middlesex at the conclusion of the current season.
It is a big boost a day after news that Chris Jordan was leaving to join Surrey and Phil Salt heading for Lancashire.
With 254 wickets in 126 appearances for England across all three formats, Finn needs little introduction.
He has featured in three Ashes winning teams, including the side that won in Australia 2010/11, was a mainstay of the England ODI side that topped the ICC ODI rankings in 2012 and played in both the 2012 World T20 and the 2015 World Cup.
During his international career, Finn has been ranked as high as number two in the ICC ODI Bowling Rankings, number five in the IT20 rankings and number 14 in the Test rankings.
In the domestic game, he has made 261 first-team appearances for Middlesex after making his debut as a 16-year-old in 2005. During that time, he has taken nearly 600 wickets across all formats.
He was part of the side that won the 2016 County Championship, has regularly captained the Middlesex T20 team over the past two seasons and was their one-day skipper for the 2018 campaign.
After signing his contract with Sussex, Finn said: “I am looking forward to the opportunity to play for Sussex from the 2022 season onwards. It is a club that I have always admired and found to be challenging opponents.
“The squad is full of exciting talent, and I can’t wait to work hard and help the team realise its full potential.”
Reacting to Finn's impending arrival at The 1st Central County Ground, Sussex Championship and One-Day Head Coach Ian Salisbury, said: “It’s fantastic to be able to attract a player of Steven’s calibre to Hove.
“He really likes the project we’ve got going on down here and is very keen to use his performances and impart all his knowledge to help us get to where we want to be in two- or three-years’ time: competing on all fronts. Steve knows all about winning, whether with Middlesex or England.
“Finny is someone who can play in all three forms in the game, and that is a big part of our strategy for new signings. He’s still a young man with plenty of good years ahead of him.
“He has a wealth of experience at the highest level with England, he’s a leader who can help develop our young players coming through and above all he is a really good guy.
Sussex’s T20 Head Coach, James Kirtley added: “I am delighted we have managed to sign Steven Finn. He is the marquee bowler we were looking for. We knew we needed to find someone to lead and support our bowling unit and we were clear we wanted a bowler of Finny's calibre in our side.
“We are also looking for leaders and he has recently led Middlesex in T20 cricket so to add this to the pot is amazing. It is important for us to have a bowler with Steve's experience to help develop our young crop of pace bowlers.
“We have talked at length about bowling, and I am very excited and looking to working with him. Steve is very keen to perform for Sussex, he really likes what we are doing, and was adamant he wanted to help our young bowlers.
“Most importantly, he is the right person for Sussex. He is an excellent bloke with a great reputation, and we are lucky to have him join us.”