The defection occurred after Ukraine's anti-corruption authorities raided Yermak's residence on Friday.
“I am an honest and decent person,” he continues in his message to the New York Post.
Jermak does not give any details about what it means that he is now "going to the front" and whether he is enlisting.
He writes that he has “been desecrated,” that his “dignity has not been protected,” and that he now does not want to cause any more problems for Zelensky.
"I am disgusted by all the crap thrown at me, and even more disgusted by the lack of support from those who know the truth," he writes.
Andriy Yermak has been one of Zelenskyy's closest associates and has been responsible for the latest peace negotiations with the United States.
At home, he has been singled out and criticized for being the president's gatekeeper with power over ministerial appointments and other key positions. His position after being drawn into the growing investigation into corruption in the energy sector became untenable on Friday.
Previously, both Justice Minister Herman Halushchenko and Energy Minister Svitlana Hryntchuk have been forced to resign due to the corruption scandal.
