Former Conservative Cabinet minister Lord Mayhew, who served as attorney general and Northern Ireland secretary during critical moments for both posts, has died at the age of 86, his family said.
In a statement, his family said he died peacefully at his home in Kent on Saturday after being unwell for several years. "He worked hard for peace in Northern Ireland," the family said.
Lord (Patrick) Mayhew of Twysden was a key figure in the December 1993 Downing Street Declaration, formulated by then prime minister John Major and then Irish taoiseach, Albert Reynolds, which led to the IRA ceasefire the following September, and is viewed as one of the most significant moments in pushing forward the peace process.
Communities Secretary Greg Clark, MP for Tunbridge Wells, said the peer would be "deeply missed".
"Patrick Mayhew, an outstanding MP for Tunbridge Wells, former Sec of State and friend has died. Much loved and respected, will be deeply missed," he said.
Baroness Stowell of Beeston, Leader of the House of Lords, tweeted: "Very sad to hear Lord Mayhew of Twysden has died. As longest-serving SoS, he played a massive part in achieving peace in N.Ireland. As a friend & colleague, Paddy Mayhew was supportive, a great source of wisdom, and always fun to be with. Condolences to his family."
Lord Mayhew, seen as being on the liberal wing of the Conservative party, was no stranger to the eye of the storm. He was solicitor-general in January 1986 and became a significant figure in the Westland crisis, which briefly threatened to endanger the position of then prime minister Margaret Thatcher.
The ex-Cabinet minister was also at the centre of controversy during the Spycatcher affair, when he attempted to block the publication of former MI5 agent Peter Wright's memoirs for the Thatcher government.
In December 2012 Lord Mayhew was praised in the House of Commons by Prime Minister David Cameron as he made a statement on the Sir Desmond de Silva report into the nature and extent of state collusion in the murder of solicitor Pat Finucane in 1989.
Mr Cameron told the Commons that de Silva found the then attorney general Lord Mayhew deserved "significant credit for withstanding considerable political pressure designed to ensure" that some prosecutions did not go ahead.
The former Cabinet minister is survived by his wife Jean Mayhew, their four sons and their families.