Max Hill QC has been named as the UK's new terror laws watchdog.
The barrister will take over from David Anderson QC as Independent Reviewer of Terrorism Legislation at the start of next month.
Mr Hill has been a QC for nine years and worked on a number of high-profile terrorism cases.
He successfully prosecuted the failed 21/7 bombers, and appeared in the inquest into the 7/7 attacks.
The Home Office said Mr Hill has "extensive experience" both defending and prosecuting complex cases involving terrorism, homicide, violent crime, high value fraud and corporate crime.
A profile on the website of his chambers said he is an "an effective multi-talented barrister who maintains a heavyweight crime practice".
Mr Hill said: "I am very pleased to have this opportunity, which comes at a time of heightened concern about the risk from terrorism which we all face in the UK.
"As a practising barrister with experience in both counter-terrorism and the rights of citizens facing allegations of serious crime, I look forward to working with participants at all levels and from all sides."
Announcing the appointment, Home Secretary Amber Rudd said: "With the threat from terrorism continuing to evolve and diversify, it is vital we have robust oversight to ensure our counter-terrorism laws are fair, necessary and proportionate.
"Mr Hill brings a wealth of experience and legal expertise to help deliver this."
The independent reviewer scrutinises the operation of the UK's laws on terrorism and produces reports.
During his six years in the role, Mr Anderson has emerged as an influential figure in the counter-terrorism sphere.
His tenure has coincided with a number of major developments, including the emergence of Islamic State and unprecedented scrutiny of the activities of intelligence services.
In 2015 he published a landmark review of surveillance powers which paved the way for the Investigatory Powers Act.
Last month Mr Anderson told the Press Association the country faces a greater threat now than when he took the post.
He said a sense of being "over the worst" when he started in 2011 had been a "false dawn".
Following the announcement of Mr Hill's appointment, Mr Anderson offered his congratulations to his "very well-regarded" successor on Twitter.
Mr Hill will begin the part-time role on March 1.