The sixth-ranked Ukrainian said in an Instagram post it was "the most difficult thing I have ever had to share".
Svitolina spoke about the tough emotional impact the war in her country had on her wellbeing, and how Monfils supported her to cope with the struggle when she took a break from tennis to recover.
"But some battles happen deep inside you, and no amount of love from someone else can win them for you," she wrote.
"With time, I came to understand that I need to find my way back to myself and that I cannot do that within our marriage."
Frenchman Monfils and Svitolina have a daughter together.
"Together, we built a beautiful life, and we were given the most precious gift of all, our daughter, Skai," Svitolina said.
"Skai will always come first. Our marriage is ending, but our family is not. We will always be her parents, side by side, at every step of her life."
The end of their marriage might have played a role in Monfils' decision to end his career a little earlier than what was expected.Â
Monfils, 40, who had planned to retire at the end of the season, is being listed by the sport's drug-testing organisation among players who have declared themselves retired, with his career officially over from October 5.
The former No.6 had been widely expected to end his career in front of his home fans at the Paris Masters from October 31.
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