The businessman has signed up to the Giving Pledge, a promise by the world's wealthiest individuals and families to dedicate the majority of their wealth to philanthropy.
With an estimated fortune of £1.1 billion, according to the Sunday Times Rich List, Lord Ashcroft said he will leave at least half of his assets to a charitable foundation in his name.
He said: "When I die, I have decided to leave the majority of my assets to a charitable foundation in my name.
"I have never been a great believer in inherited wealth.
"My family will be trustees of the foundation so that they will be able to enjoy making donations to worthy causes in my name."
The Giving Pledge, which is a moral commitment and not a legal contract, was set up by Microsoft founder Bill Gates and his wife Melinda Gates, and investor Warren Buffett. Lord Ashcroft will be added to the list of pledgers on Tuesday.
He said: "The pledge is made publicly because the founders' goal is to talk about giving in an open way and to create an atmosphere that can draw more people into philanthropy.
"I would like to see a situation in which the richest of our society believe it to be their obligation to support good causes."
However, he said he will provide for his family, believing it "a little harsh" to leave them with nothing.
Lord Ashcroft also set up Crimestoppers and helped to open a gallery of the world's largest collection of Victoria Crosses and George Crosses at the Imperial War Museum to champion bravery.