Collymore helped Sussex clinch promotion to Division One
Middlesex have signed Sussex seamer Corey Collymore on a two-year deal.
He will replace fellow former West Indies international Pedro Collins, 34, who is leaving as he no longer fits the criteria to qualify as a Kolpak player.
Barbados-born Collymore is Sussex's leading wicket-taker in the County Championship this term, taking 57 wickets at an average of 19.87.
"I'm disappointed to be leaving Sussex but it is the best decision for me and my family," the 32-year-old said.
Collymore, who played the last of his 30 Tests in 2007 and joined Sussex the following year as a Kolpak player, has taken the decision to leave the new Division Two champions to be closer to his extended family who live in London.
"I'm fortunate to have played for a very successful club over the last few years. The atmosphere has been great," he added.
"I'm hoping that the transition to Middlesex will be as smooth as when I moved from Barbados to Sussex."
Sussex cricket manager Mark Robinson said: "We respect Corey's desire to be closer to his family.
"Everyone at Sussex would like to thank Corey for his efforts. We wish him and his family all the best for the next chapter of their lives."
After signing Collymore as a Kolpak, Middlesex managing director of cricket Angus Fraser explained why left-arm seamer Collins no longer qualifies under the ruling, which allows players from countries with associate trade agreements with the European Union not to be classed as "overseas" players.
"It is more than five years since Pedro played his last Test for the West Indies, and he has only played in England as a Kolpak player for three seasons, when the regulations state that it needs to be four," Fraser told Middlesex's website.
"Pedro has been outstanding both on and off the field, and he will be missed. Corey is cut from the same cloth. He is proud and hard-working and we can expect his input to be just as valuable as Pedro's."
Collins played the last of his 32 Tests for the Windies in July 2006.