The actor had reportedly been diagnosed with cancer.
Willie played the flamboyant talent agent and close friend and confidante of Sarah Jessica Parker’s Carrie Bradshaw in Sex And The City from 1998 until the show ended in 2004.
He reprised the role in the two Sex And The City films and had been working on the spin-off series And Just Like That.
While his best known character was a gay man, the actor was straight.
Cynthia Nixon, who plays Miranda Hobbes in Sex And The City, shared a tribute on Twitter.
She said: “So deeply, deeply sad we have lost @WillieGarson. We all loved him and adored working with him. He was endlessly funny on-screen and in real life. He was a source of light, friendship and show business lore. He was a consummate professional— always.”
She sent her condolences to Garson’s adopted son, Nathen.
Kristen Davis, who plays Charlotte in Sex And The City, said Willie was “smarter and funnier than you ever would have imagined”, adding that she was “bereft” at the news of his death.
Kim Cattrall, who won a Golden Globe for her turn as Samantha Jones, also shared a tribute, writing: “Such sad news and a terribly sad loss to the SATC family. Our condolences and RIP dear Willie xo”
Michael Patrick King, executive producer of Sex And The City and And Just Like That, said Willie had been dedicated to his work even while ill.
He said: “The Sex And The City family has lost one of its own. Our amazing Willie Garson.
“His spirit and his dedication to his craft was present every day filming And Just Like That. He was there — giving us his all — even while he was sick. His multitude of gifts as an actor and person will be missed by everyone. In this sad, dark moment we are comforted by our memory of his joy and light.”
Mario Cantone played Wiilie’s on-screen partner in Sex And The City.
He said: “I couldn’t have had a more brilliant TV partner. I’m devastated and just overwhelmed with Sadness. Taken away from all of us way soon. You were a gift from the gods. Rest my sweet friend. I love you.”
A spokesperson for HBO and HBO Max said: “Willie Garson was in life, as on screen, a devoted friend and a bright light for everyone in his universe.
“He created one of the most beloved characters from the HBO pantheon and was a member of our family for nearly twenty-five years.
“We are deeply saddened to learn of his passing and extend our sincere condolences to his family and loved ones.”
Actor Titus Welliver, a close friend of Garson, was one of the first to share a tribute.
He tweeted: “There are no words. I love you dear brother. We are fewer.”
Rob Morrow, the actor, said: “Our sweet pal #WillieGarson has passed on. Dear soul, rest easy.”
As well as Sex And The City, which originally ran from 1998-2004, Willie was known for his role as Mozzie in police procedural White Collar.