The family said in an announcement he died "peacefully" Friday night.
McAlpine, who became Baron McAlpine of West Green when he was elevated to the House of Lords in 1984, was known as a dedicated fundraiser who raised millions of pounds for the Conservatives, the Daily Telegraph reported. He defected to the Reform Party in the late 1990s and served as its leader before rejoining the Conservatives.
McAlpine, who suffered from dyslexia, left school without any qualifications to work for the building company founded by his great-grandfather. He rose quickly to become a director, showing considerable business acumen.
Thatcher named him joint treasurer of the Conservative Party in 1975 and deputy director of the party after the election of 1979, which made her prime minister.
In addition to raising money, McAlpine convinced the department store chain Marks & Spencer to donate clothes to the victims of the 1984 Brighton Hotel bombing, which occurred during a party conference.
Outside of politics, McAlpine was known for his wide interests, including art and the welfare of Australia's aboriginal population.
"He had always got something interesting to say," Norman Tebbit, a former Conservative minister and colleague in the House of Lords, told the BBC. "A very cultured man, very interested in the arts, also much-traveled. He seemed to find a quite natural home in Italy in recent years."