The 37-year-old, who has had two knee surgeries since 2023, downed American Learner Tien 7-5 7-6(4) at the Dallas Open on Tuesday to reach the milestone, putting him second behind Novak Djokovic (1,168 wins) among active players.
"It's been so difficult these last couple of years, I was battling through many things," said Cilic, who also went past Croatian compatriot Goran Ivanisevic's career tally of 599 tour-level victories.
"Just to get to this level, playing this well against guys like Learner, who's an incredible player and can have a fantastic career, is just a joy.
"To get this milestone speaks volumes about my dedication to tennis, living in this sport for so many years. It's given me so much joy and I love it. It's fun to be out here still competing and I can't be happier."
Cilic, who claimed his only Grand Slam trophy at Flushing Meadows in 2014, tore the lateral meniscus on his right knee in 2023 and underwent surgery. That was followed by another in 2024 following difficulties in his recovery.
The former world number three bounced back on the biggest stage by reaching the fourth round of Wimbledon last year and the third round of the Australian Open last month.
Cilic will face another American in Dallas with either Trevor Svajda or Ethan Quinn up next.
