P&G's stock was up 4% in after-hours trading on the news.
Trian is the second activist hedge fund to invest in P&G in recent years. In 2012, Bill Ackman's Pershing Square invested, leading to then-CEO Robert McDonald to step down within a year, the Journal reported.
P&G is the maker of everything from Gillette to Crest to Pantene to Tampax.
Peltz said in December that he had taken a new position but did not disclose which company it was in. His firm raised a special fund in recent months exclusively for its P&G position, according to the Journal report.
A number of other hedge funds disclosed new positions in 13-F filings on Tuesday.