The pace bowler, who has made 126 appearances for England across three formats, leaves Middlesex after 17 years as a player
Steven Finn will leave Middlesex at the end of the 2021 season to join Sussex.
The pace bowler has spent 17 years with Middlesex, making his debut against Cambridge University as a 16-year-old in 2005, becoming their youngest first-class debutant in the process.
In total, Finn has made 109 first-class appearances for Middlesex, taking 394 wickets at an average of 28.13 and winning the County Championship title in 2016. With the white ball, he has made a further 152 appearances, taking 77 wickets at 28.14 in List A cricket and 116 wickets at 22.25 in 93 T20s.
The 32-year-old has also represented England on 126 occasions – 36 Tests, 69 ODIs and 21 T20Is, taking 254 wickets. He featured in three Ashes winning teams, was a mainstay of the England side which topped the ICC ODI rankings in 2012 and played in both the 2012 World T20 and 2015 Cricket World Cup.
Commenting on his departure from Middlesex, Finn said: "I feel incredibly fortunate to have played for Middlesex for seventeen seasons since my debut in 2005 and have made countless lifelong friends.
"It has been more than a club. It has been a family, and I will always be grateful for the support I have received from players, coaches, staff, and board members.
"Every time I have set foot on the field for the club, I have given my all, and even though results have been tough recently, I see a bright future for the club.
"Now, as I move into the last stage of my career, it seems the right time to embrace a completely new challenge and I am excited and enthused by the prospect of helping a talented, young Sussex team realise their potential."
Discussing his new signing, Sussex’s Championship and One-Day coach, Ian Salisbury, added: "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."