Garson was born in Highland Park, New Jersey, the son of Muriel (née Schwartz) and Donald M. Paszamant. Garson was Jewish. He attended Camp Wekeela in Hartford, Maine, as a child for 11 years. He graduated in 1982 from Highland Park High School. In 1985, he received a Bachelor of Fine Arts degree in Theater from Wesleyan University and a Master of Fine Arts degree from the Yale Drama School.
Garson began his career in theater, appearing in productions off-Broadway and on Broadway. He made his film debut in the 1989 comedy Troop Beverly Hills. He had his breakthrough role in 1998 as Stanford Blatch on Sex and the City. He played the role for the entire six-season run of the show and in the two subsequent films.
Garson continued to work steadily in film and television throughout his career. He appeared in numerous other films, including The Rock (1996), There's Something About Mary (1998), and The Wedding Planner (2001). He also had recurring roles on the television shows NYPD Blue (1993), Friends (1995), and Hawaii Five-0 (2010).
Garson was a talented actor who was known for his versatility and his ability to play a wide range of characters. He was also a gifted comedian and a scene-stealer. He will be remembered for his roles in Sex and the City, White Collar, and other films and television shows.
Garson died on September 21, 2021, at the age of 57. He had been diagnosed with pancreatic cancer earlier that year.