Former U.S. attorney Ronald C. Machen Jr., left, and Vincent H. Cohen Jr., who is joining the Dechert law firm. (Sarah L. Voisin/The Washington Post)

The city’s former top prosecutor, Vincent H. Cohen Jr., has joined the Dechert law firm as a partner in its litigation group in Washington. Cohen, who oversaw a series of high-profile public corruption investigations in the District, will represent individuals and companies in “high-stakes litigation,” such as “sensitive government and internal investigations, government enforcement matters, and complex civil and criminal litigation,” according to the firm’s website.

Andrew J. Levander, chairman of the firm’s policy committee, said in a statement that Cohen’s experience “at the highest levels of government provides him with a sophisticated and unique background that will allow him to handle our clients’ most challenging legal problems.”

At the U.S. attorney’s office, Cohen was the principal assistant to former U.S. Attorney Ronald C. Machen Jr., who led the long-running probe into former D.C. mayor Vincent C. Gray’s 2010 campaign. Cohen served as acting U.S. attorney after Machen stepped down in April, and he had hoped to succeed him.

But Del. Eleanor Holmes Norton (D-D.C.) recommended veteran Justice Department official Channing D. Phillips for the job. Cohen was asked repeatedly during the interview process by a commission advising Norton about the status of the investigation and why it was taking so long, according to two people who took part in the interview.

Phillips, who was nominated in October, announced last month that the office was shutting down the probe, meaning that Gray would not be charged.

Cohen’s partner position is a return to the private sector, where he worked from 2003 to 2010, practicing civil and criminal law at an international law firm and later at a boutique firm specializing in high-stakes litigation.