Facebook’s chief information security officer, Alex Stamos, will leave the company after internal disagreements over how the social network should deal with its role in spreading disinformation, according to current and former employees briefed on the matter.

Mr. Stamos had been a strong advocate inside the company for investigating and disclosing Russian activity on Facebook, often to the consternation of other top executives, including Sheryl Sandberg, the social network’s chief operating officer, according to the current and former employees, who asked not to be identified discussing internal matters.

After his day-to-day responsibilities were reassigned to others in December, Mr. Stamos said he would leave the company. He was persuaded to stay through August to oversee the transition of his duties because executives thought his departure would look bad, the current and former employees said. He has been overseeing the transfer of his security team to Facebook’s product and infrastructure divisions. His group, which once had 120 people, now has three, the current and former employees said.