Tuesday night's event was the first time the candidates in the Nov. 5 presidential election had met face to face.
The viewing figure tops the roughly 51 million people who watched Trump debate then-candidate President Joe Biden in June.
It does not capture the full extent of online viewing, which has grown in popularity as traditional TV audiences decline.
The record TV audience for a presidential debate occurred in 2016, when 84 million people tuned in to watch Democratic candidate Hillary Clinton debate Trump.
