Ron Reagan, son of the late Republican president, is to address the Democratic Party National Convention which begins on 26 July in Boston.
Nancy and Ron Reagan are passionate advocates of stem cell research
Mr Reagan said he would speak about the role of stem cell research in finding cures for diseases like Alzheimer's.
Ronald Reagan died on 5 June a decade after announcing he had the disease.
The Bush administration has limited public funding of this type of research because of ethical reservations about using stem cells from human embryos.
The use of embryonic stem cells is controversial because a living human embryo is destroyed in order for the cells to be extracted.
But Mr Reagan, 46, told the Philadelphia Inquirer newspaper that the Democratic Convention would give him an important platform to educate people about the issue.
"The conservative right has a rather simplistic way of characterising it as baby killing. We're not talking about fingers and toes and brains. This is a mass of a couple hundred undifferentiated cells," he said.
In May this year, Mr Reagan's mother Nancy, the former first lady, publicly urged President George W Bush to reverse his stem cell policy.
The president has cut federal funding for such research, citing ethical concerns about performing experiments with fertilised human embryos.
The Democratic Party platform calls for lifting restrictions on such research.
Mr Reagan, an outspoken critic of the Bush administration, said he would not campaign for the Democratic presidential candidate, John Kerry, but that he would vote for him "as a way to defeat Bush."
He told the Philadelphia Inquirer he expected criticism from many Republicans for his speech to the Democrats but said he was not a Republican and never had been.
"My father wouldn't expect me to be a Republican just to emulate him."