What a difference a year makes.
In 2013, Bill Ackman was accused of losing his golden touch. His investment in J.C. Penney was called a "fiasco." His Herbalife short famously turned against him when fellow activist investors Carl Icahn and Dan Loeb took the other side of the trade. Pershing Square Capital Management's assets fell as performance was barely positive into the fall.
This year is different. Late Monday, news broke that Ackman and Valeant Pharmaceuticals were offering to buy Botox maker Allergan. Shares of Allergan, of which Pershing Square owns 9.7 percent, immediately gained about 23 percent.
That's not the only winner: Every Ackman investment appears to have made money this year, including Beam, the Herbalife short and Platform Specialty Products Corp. Nutritional supplement maker Herbalife, for example, has been hit by reports of several government investigations into the company, which has helped push the stock down about 26 percent so far in 2014.
The Pershing Square International fund is up 11.1 percent net of fees in the first quarter alone, according to a report by the HSBC Alternative Investment Group.
A spokesman for Pershing Square declined to comment.
"We think Bill is having a great year and are happy to see several situations where his activist work has helped create significant value for shareholders," said Gregg Hymowitz, managing partner of EnTrust Capital, an $11 billion fund of hedge funds that has money with Pershing Square on behalf of clients.
"The acquisition of Beam, which connects back to his work at separating Fortune Brands started a few years ago, will go down as a great activist case study. Additionally, his latest position with Allergan is possibly starting the newest trend in activism, proving yet again that he can be a very thoughtful investor."
One Pershing Square client who asked not to be named cautioned that recent performance swings were fleeting. "We are long-term investors. One year is but a small moment in time," the person said.
"We are very happy about it thus far," the client added.
For all the bad news last year, Pershing Square gained 9.3 percent, according to the HSBC report. The Absolute Return Event Driven Index, which tracks similar activist hedge funds, rose 14 percent in 2013. The International fund's net annualized return since December 2004 is 16.58 percent, according to HSBC.
Pershing Square managed $13 billion as of April 1, up from $12 billion in February.
—By CNBC's Lawrence Delevingne.