That would make it the second most-watched political debate ever, behind only the 80.6 million people who watched President Jimmy Carter and challenger Ronald Reagan in their only 1980 encounter, according to Nielsen Media Research.
When John McCain and Barack Obama met in their first debate on Sept. 26, Nielsen recorded 52.4 million viewers. They will have two more debates, the first of them next Tuesday.
Palin has been a television star since joining the GOP ticket a month ago. The curiosity factor undoubtedly brought in viewers this week after Palin raised doubts about her readiness for the job with some wobbly TV interviews.
Most analysts said she erased some of those doubts Thursday but didn't necessarily win the debate or bring more voters into the McCain camp.
Timing may also have played a part in the big ratings. Thursday is one of the most popular nights of the week for TV-watching, while Friday, when McCain and Obama first debated, is one of the least popular.
Generally, only Super Bowls bring together so many Americans to watch the same thing.
Nielsen estimated that 69.99 million people watched Palin and Biden on either ABC, CBS, NBC, Fox, CNN, Fox News Channel, MSNBC, CNBC, BBC America, Telemundo or TeleFutura. The figure does not include PBS or C-SPAN, which also showed the debate, but PBS estimated its audience at 3.5 million.
The audience far exceeded any other vice presidential debate.The closest was in 1984, when Geraldine Ferraro was the first woman on a major-party ticket, and 56.7 million people watched her and Vice President George Bush.
ABC claimed a pundit victory. Its audience for the half hour of post-debate analysis Thursday was larger than that of NBC or CBS.