The left-handed Pooran had recently opted out of selection for West Indies' T20I series in England after participating in the Indian Premier League (IPL).
He finishes his international career having scored 1983 runs in 61 ODIs and 2275 runs in 106 T20Is.
Pooran wrote in statement on social media: "After much thought and reflection, I've decided to announce my retirement from international cricket. This game we love has given and will continue to give so much - joy, purpose, unforgettable memories, and a chance to represent the people of the West Indies.
"Wearing that maroon, standing for the anthem, and giving everything I had each time I stepped on the field... it's hard to put into words what that truly means to me. To have led the team as captain is a privilege I will always hold close to my heart.
"To the fans - thank you for your unwavering love. You lifted me in the tough moments and celebrated the good ones with unmatched passion.
"To my family, friends and teammates - thank you for walking the journey with me. Your belief and support carried me through it all. Though this international chapter of my career closes, my love for West Indies Cricket will never fade.
"I wish the team and the region nothing but success and strength for the road ahead."
Cricket West Indies said: "Cricket West Indies extends sincere gratitude and appreciation to Nicholas Pooran for his outstanding contributions to West Indies cricket.
"We salute his achievements and thank him for the moments he has given fans across the region and beyond. We wish him all the very best in the next phase of his journey."
Proteas Women produced a clinical all-round performance to secure a 40-run victory over the West Indies in the second ODI in Barbados on Saturday, leveling the three-match series 1–1 with one game to play.
West Indies coach Daren Sammy has described Nicholas Pooran's unexpected retirement from international cricket as a sign of a broader challenge facing Caribbean cricket, predicting more players may soon follow.
England sealed a T20 international series win over the West Indies after successfully chasing down a target of 197 to win the second match in Bristol on Sunday.
England allrounder Jamie Overton has been ruled out of the remainder of the white-ball series against West Indies after sustaining a fractured right little finger during the first ODI at Edgbaston.
