Singer has been a prominent advocate of gay-rights initiatives, donating more than $10 million in the past. He was among one of the biggest financial supporters of New York state's gay marriage law.
Polls in the aftermath of President Obama's decision to support gay marriage show that more than half of Americans generally agree with the president. Nearly three quarters of respondents between 18 and 34 years old said they supported the practice in a CNN/ORC poll released Wednesday.
Mitt Romney, however, has repeatedly said he believes marriage should be between a man and a woman.
"My view is that marriage itself is a relationship between a man and a woman. And that's my own preference," Romney said last month while campaigning in Nebraska. "I have the same view that I've had since running for office."