Northern Ireland-born judge Lord Hutton is to retire as a Law Lord.
Lord Hutton is to step down in the new year
The former Lord Chief Justice in Northern Ireland will step down in January shortly before he publishes his report into the death of weapons expert Dr David Kelly.
The 72-year-old peer's retirement will have a knock-on effect for the judiciary in the province.
The current Lord Chief Justice of Northern Ireland, Sir Robert Carswell, is to become a Law Lord on 12 January.
His duties will include sitting in the House of Lords and hearing final appeals on legal cases.
Sir Robert Carswell will be replaced by Sir Brian Kerr as Lord Chief Justice in Northern Ireland.
Lord Hutton, who is a crossbench peer, heard evidence into Dr Kelly's death during the summer.
A statement on the Hutton Inquiry website said his retirement would have no effect on his work in writing his report on the six-week inquiry.
Lord Hutton is expected to issue his report to Lord Falconer, the Lord Chancellor, in January.
Meanwhile, Mr Justice Kerr said on Thursday that he was deeply honoured to be replacing Sir Robert Carswell in charge of Northern Ireland's courts.
He said he looked forward to meeting the challenges posed by his new role.
"The justice system is in a period of considerable change. As judges we recognise that we must play our part in the implementation of those changes," he said.
Sir Brian Kerr is the new Lord Chief Justice in Northern Ireland
"For instance, we will be participating in the establishment of a new Judicial Appointments Commission and will be dealing with the many legislative initiatives that will have an impact on the work of the courts.
"I am confident that the judiciary will rise to the challenge that these changes present while continuing to manage the ongoing and significant workload undertaken in courts at every level."
Mr Justice Kerr has been a High Court judge since 1993.
He was educated at St Colman's College in Newry, County Down, and at Queen's University in Belfast.
He was called to the Bar in Northern Ireland in 1970 and in England four years later.
He took silk in Northern Ireland in 1983 and he was appointed a Senior Crown Counsel in 1988.