In a letter to the president posted to Icahn's website, the billionaire investor said the decision came after a Friday conversation between the two men. Icahn wrote that he made the decision with the president's blessing.
The famed investor said he resigned from the role to avoid "partisan bickering" about his position. Icahn said he did not want that scrutiny to affect the Trump administration's work on regulatory reform.
The billionaire had been a frequent critic of Obama-era rules. He previously said the EPA was one of the worst-run agencies he had ever seen.
Icahn also took the opportunity to again insist that he "never had a formal position with your administration nor a policymaking role." He reiterated that his advisory position did not give him access to nonpublic information.
Those statements referenced skepticism from Democratic lawmakers regarding Icahn's informal advisory role. Some Democrats had asked regulators to look into whether Icahn, a major fossil fuel investor, had engaged in any improper market behavior.
Read Icahn's full letter to Trump below:
"Dear Mr. President:
This will confirm our conversation today in which we agreed that I would cease to act as special advisor to the President on issues relating to regulatory reform.
As I discussed with you, I've received a number of inquiries over the last month regarding the recent appointment of Neomi Rao as Administrator of the Office of Information and Regulatory Affairs (or "regulatory czar," as the press has dubbed her) – specifically questions about whether there was any overlap between her formal position and my unofficial role. As I know you are aware, the answer to that question is an unequivocal no, for the simple reason that I had no duties whatsoever.
I never had a formal position with your administration nor a policymaking role. And contrary to the insinuations of a handful of your Democratic critics, I never had access to nonpublic information or profited from my position, nor do I believe that my role presented conflicts of interest. Indeed, out of an abundance of caution, the only issues I ever discussed with you were broad matters of policy affecting the refining industry. I never sought any special benefit for any company with which I have been involved, and have only expressed views that I believed would benefit the refining industry as a whole.
Nevertheless, I chose to end this arrangement (with your blessing) because I did not want partisan bickering about my role to in any way cloud your administration or Ms. Rao's important work. While I do not know Ms. Rao and played no part in her appointment, I am confident based on what I've read of her accomplishments that she is the right person for this important job.
I sincerely regret that because of your extremely busy schedule, as well as my own, I have not had the opportunity to spend nearly as much time as I'd hoped on regulatory issues. I truly appreciate the confidence you have in me and sincerely hope that the limited insights I shared have been helpful to you. I love our country which has allowed me to achieve so much and I thank you for the informal opportunity you have given me to aid it.
CARL C. ICAHN"