Clifford Chance New York white collar partner Ed O'Callaghan has left the firm to join the US Department of Justice.

O'Callaghan started his new role – as principal deputy assistant attorney general – today (13 November) in the DOJ's National Security Division. He will responsible for helping to shape US national security and enforcement priorities.

He exits after six years, having joined in 2011 as a partner in the firm's government investigations and white collar criminal defence practice.

Previously, O'Callaghan worked for US firm Nixon Peabody for just over two and half years, where he headed up the firm's government investigations and white collar defence group.

Before that, he worked for the US Attorney's Office for the Southern District of New York, where he was co-chief of the terrorism and national security unit.

During his time with CC, he represented senior executives and officials of JP Morgan in connection with $6.2bn (£4.7bn) of trading losses in 2012; O'Callaghan acted for Achilles Macris, who was head of the London branch of JP Morgan's chief investment office, where the trader nicknamed the "London Whale", Bruno Iksil, worked.

He also acted for former top FIFA official Jeffrey Webb, who was arrested for corruption charges in 2015. Webb, who pleaded guilty later that year, was among several officials arrested in 2015 on corruption charges following an inquiry by the Federal Bureau of Investigation (FBI).

In addition, he helped secure a major win in Washington, DC for Dutch aerospace firm Fokker Services in 2014, in a case relating to alleged US sanctions violations.

A CC press spokesperson said: "Although he will be missed by our firm, this is a great opportunity for Ed as he returns to government service…We want to thank Ed for his many substantive contributions to our firm, notably in connection with high-profile global investigations."