Musk confirmed the move in a tweet, adding that the account of satirical website Babylon Bee was also reinstated.
The new billionaire owner misspelled Griffin and Peterson's names in his tweet.
Musk said in May he would reverse Twitter's ban on Trump, whose account on the social media platform was suspended after last year's attack on the U.S. Capitol.
The Tesla Inc chief earlier this month said Twitter users engaging in impersonation without clearly specifying it as a "parody" account would be permanently suspended without a warning.
The comment came as Griffin's account was banned earlier this month after the U.S. comedian changed her name to Elon Musk. The #FreeKathy hashtag was later circulating on Twitter.
Twitter had also paused its recently announced $8 blue check subscription service last Friday as fake accounts mushroomed.
The fake accounts purporting to be big brands, included those of Musk's Tesla and SpaceX, as well as Roblox, Nestle and Lockheed Martin.
(Reporting by Tiyashi Datta in Bengaluru; Editing by Shailesh Kuber)
