Paul Stirling will leave Middlesex at the end of the season after committing his future to Ireland.
With Irish players no longer qualifying as non-overseas players in county cricket from next year, it had been suggested that players like Stirling would renew their county contracts and give up international cricket.
But Stirling - who captained Ireland in T20 cricket earlier in the year - has signed a new international contract, ending ten years of association with Middlesex.
Stirling said: "It's been a real privilege to represent Middlesex over the last decade, and it has been an unforgettable journey for many reasons. Winning the Championship in 2016 was undoubtedly the highlight on the field, while also receiving my county cap will be something I will cherish for a very long time.
"However, it was the relationships built with the players, staff and supporters that was the most rewarding, and that I will miss the most.
"I am looking forward to the next chapter with Ireland, with a busy year in 2020 and the T20 World Cup Qualifier coming up it is an exciting time to be a part of."
Angus Fraser, Middlesex's director of cricket, said that everyone at the club "fully respects Paul's decision" and that the coaching staff fully understood the reasoning behind it.
"From a selfish and Middlesex point of view it is obviously sad to see Paul leave," said Fraser. "His aggressive and destructive batting has thrilled Middlesex players and supporters for a number of years.
"The Middlesex coaches and myself totally understand Paul's decision. It has not been an easy one and I know he has thought about it long and hard. Playing for your country is something that should never be taken for granted. It is an honour and a privilege, and to finish a career with regrets is something nobody wants to do.
"He will always be welcome at Lord's and if he ever feels like coming back to play for us in any capacity he has my phone number."
Stirling's team-mate Tim Murtagh is yet to make a decision whether to continue playing international cricket or whether to renew his Middlesex deal.
"It's getting to the stage where we have to choose one or the other and I haven't really made my mind up yet," Murtagh told the Wisden Cricket Weekly podcast in August.
"There are still discussions to be had with both sides but unfortunately that loophole has been shut and we can't continue playing in county cricket as local players. I'm going to have to make quite a tough decision at the end of the summer and decide which way I want to keep going."