The top lawyer for the National Security Agency, Rajesh De, has stepped down from his post and will join the law firm Mayer Brown.

De’s last day was Friday, and he plans to start at Mayer Brown in June as head of the firm’s privacy and security practice in Washington. He had been NSA’s general counsel since April 2012 and oversaw the exposure of the government’s controversial surveillance program by former NSA contractor Edward Snowden.

“It’s a natural time to move on,” De said.

The NSA’s deputy general counsel Teisha Anthony will be the acting general counsel until a permanent replacement is named. De defended the NSA’s practices during his three-year tenure, arguing that the agency has acted within the legal and policy framework provided by the executive branch, Congress and the courts.

But he said that “reasonable people can have an intelligent and thoughtful discussion about what they want that framework to look like.” De said he hopes Congress, which has a June deadline to reauthorize Section 215 of the Patriot Act — the provision that grants the NSA legal authority to collect Americans’ phone records — will reach a resolution that allows the government to preserve the operational capabilities it needs to maintain national security, while also addressing the need to move the metadata out of the government’s hands.

De declined to comment specifically on Snowden, other than to say that he believes no one should consider themselves above the law. “No person, a king or an IT guy, should consider themselves above our democratic system,” De said. “There’s a legal process we all adhere to. None of us is above the system.”

In his new role, De — who was a partner in Mayer Brown’s litigation group before joining the government — will advise companies in the financial services, health-care, retail and manufacturing sectors on data privacy and cybersecurity issues. He said he has not decided whether he will register as a lobbyist.

De held a number of senior roles in the Obama administration over the past six years, including staff secretary and deputy assistant to the president, principal deputy assistant attorney in the Justice Department’s Office of Legal Policy, and counsel to the 9/11 Commission.

De is joining Mayer Brown at a time when law firms are clamoring to grow their data privacy and cybersecurity practices. A number of major firms, including DLA Piper and Pillsbury, have bulked up their cybersecurity capabilities in recent months.

“Privacy and cybersecurity is probably the number one issue clients have been asking us about over the last year,” Mayer Brown Chairman Paul Theiss said. “It’s certainly the fastest-growing.”

De said he is especially interested in working with Mayer Brown’s clients to prevent data breaches, and to advise them in the regulatory and litigation-related consequences that may follow if and when a breach occurs. “Between foreign adversaries, hackers, modern-day thieves...this is a real challenge not just for governments but the private sector as well,” he said.