Mr Iain Duncan Smith was tonight elected leader of the Conservative Party to succeed Mr William Hague, easily beating off rival Kenneth Clarke.
Mr Duncan Smith polled 155,933 votes to Mr Clarke's 100,864, a 61% to 39% share of the vote on a 79% turnout of 256,797 Tory members.
A Conservative spokesman said later the result was a "ringing endorsement" of Mr Duncan Smith.
The new leader's first move was to appoint one-time rival candidate Mr David Davis as party chairman, with party sources describing the MP for Haltemprice and Howden, East Yorkshire, as "a street fighter who will take the battle to Labour".
Mr Davis is also understood to have been given a key role in policy development as the Tories struggle to overhaul Labour's massive Commons majority at the next election.
At a low-key announcement of the election result tonight, postponed for 24 hours in the wake of the US terror strikes, Mr Duncan Smith first paid tribute to his rival Mr Clarke, then pledged support for the Government in backing America's response to Tuesday's tragedy.
The new leader also promised to focus on the state of the public services, saying: "The party I lead will be an effective opposition to this Government.
"It will campaign on the issues that really matter to people, the things that affect them most in their daily lives, obsess them, these are the things that must obsess us.
In response to the outrages in the US, he added: "What President Bush called an act of war must not go unpunished.
"My party will stand shoulder to shoulder with the Prime Minister and his government in supporting our friends and allies in the United States during this tragic time."
PA