Peltz, CEO of Trian Fund Management, was also rebuffed in a battle for board seats, or proxy contest, at DuPont two years ago. But he went on to attract more money from investors and have a key ally installed as the chemical maker's new chief executive.
Trian said on Tuesday that the shareholder vote at P&G, the biggest company to ever face a proxy contest, was too close to call, and that it would wait for the result to be certified by an independent inspector. P&G says Peltz has lost.
But if Peltz's defeat is confirmed, there is little evidence it would cost him with his investors, industry analysts and academics said.
"Overall, Nelson Peltz has a good record and he does work hard to improve companies," said University of Michigan professor Erik Gordon. "He will have no trouble finding companies where improvements need to be made and where he'll be let in the door."
Trian's assets under management are at an all-time high of $14 billion, the result of long-standing confidence by pension funds and endowments in Trian's 12-year investment history. There was no sign on Tuesday of significant redemptions by Trian investors.
Indeed, Trian got a boost this week from another big U.S. conglomerate, when General Electric Co offered a board seat to Trian chief investment officer Ed Garden, without any proxy contest.
To be sure, Trian was eager for a win at P&G. Trian's 2.1 percent return through the end of September trails the average activist hedge fund's 4.8 percent gain this year. And it lags last year's 11 percent return.
Trian prefers to work behind the scenes and has only waged three proxy contests since its founding in 2005. It now looks to have lost two of them, and joins a small club of activist hedge funds that have experienced such defeat. They include Bill Ackman's Pershing Square Capital Management, Barry Rosenstein's Jana Partners and Jeff Smith's Starboard Value.
In the investment community, 75-year old Peltz, who speaks in calm tones and steers clear of the name-calling often heard in other contests, was thought to be the only activist who could take on P&G and its entrenched management.
However, the 180-year-old company, which makes Tide detergent, Crest toothpaste and Gillette razors, always presented a challenging target for Peltz because an unusually high 40 percent of P&G's stock is held by individual investors. They include P&G employees and retirees, who are traditionally loyal to the company's management.
"Even if they win, which I'm not sure they did, think of what a pyrrhic victory it is," Peltz told CNBC on Tuesday. "I mean everybody but the current employees voted for us up and down the line."
P&G cannot afford to ignore Peltz even if victory has eluded him on this vote, said Charles Elson, a professor of corporate governance at the University of Delaware.
"In many ways, this could echo what happened at DuPont, where within the year, the CEO was out and the things Trian called for were happening," he said.
On Tuesday P&G's share price fell, closing down 0.5 percent, as investors worried whether the company would let up on its promises to pursue operational reforms.
P&G has said that management is already working on several operational changes, and that Peltz does not have the relevant experience to be helpful in the process.
Investor pressure could still deliver change, industry insiders said.
"Winning the 'war' will be measured in the share price creation over time," said Bruce Goldfarb, founder of Okapi Partners, which advises on proxy contests.
(Reporting by Svea Herbst-Bayliss in Boston, Editing by Rosalba O'Brien)
By Svea Herbst-Bayliss