Minnesota Timberwolves forward Kevin Garnett has announced his retirement after 21 NBA seasons, leaving behind a legacy of ultimate intensity and defensive prowess.

The T-Wolves legend, who won his lone NBA championship ring as a member of the 2008 Boston Celtics, brought down the curtain on his career via a farewell video on Instagram on Friday.

"I'm just thankful man, I can't ever ever put that into words," the 40-year-old said. "I'm just thankful to everybody and the love. I never would've thought that people would love me like this. For it to be a reality is just something else."

Garnett's departure is the latest in a year which also saw future Hall of Fame players Kobe Bryant and Tim Duncan bid adieu to the NBA.

The Minneapolis Star Tribune reported that Garnett, who was signed for $8million this season, had reached a contract settlement with the Timberwolves.

"It has been a real joy to watch KG come into the league as a young man and watch him develop his skills to become one of the very best in the NBA," Timberwolves owner Glen Taylor said in a statement.

"I have treasured the opportunity to see him grow as a leader. I wish him continued success in the next chapter of his life. His Minnesota fans will always cherish the memories he has provided."

Garnett, easily the most productive player in franchise history, spent 13 1/2 of his 21 NBA seasons with Minnesota.

He was drafted out of high school in 1995 and his success helped usher in an era of players foregoing college to leap into the NBA - LeBron James and Bryant chief among them.

Garnett earned more than $330million in his career, the most by any player in league history, but it was his intensity as well as his pay and production that earned him the nickname "The Big Ticket".

He was one of basketball's indelible personalities, known for his constant trash-talking and emotion. His pre-game ritual involved bumping his head on the basket support while muttering to himself.

After the tip-off, he was one of the most versatile power forwards in NBA history, showcasing his ability to dribble, shoot, pass and guard every position on the court despite being nearly seven-feet tall.

A 15-time All-Star, Garnett ranks 17th with 26,071 career points, ninth in career rebounds with 14,662 and 17th in blocked shots with 2,037.

Garnett spent his first 12 seasons in Minnesota, capturing the league's MVP in 2004, before joining the Boston Celtics where he cemented his status by leading them an NBA championship in 2008.

He spent a short stint with the Brooklyn Nets before returning to Minnesota in 2015 to finish his stellar career back where it all started.