The company reported Thursday that Roberts had resigned as the executive editor and anchor of Global Toronto and as the co-host of The Morning Show.
Roberts had not disclosed his involvement in the company to Global.
On Thursday, Global published Roberts's resignation letter on its website.
"I regret the circumstances, specifically a failure to disclose information, which led to this outcome," Roberts said in the letter.
The Toronto Star recently revealed that Roberts was a part-owner of Buzz PR and that some of that company’s clients had appeared on his show.