Pershing Square Capital Management
In 2004, with $54 million from his personal funds and from his former business partner Leucadia National, Ackman started Pershing Square Capital Management.
In 2010, Pershing Square started buying J. C. Penney shares, paying an average of $22 for 39 million shares or 18% of J.C. Penney's stock. In August 2013, the two-year campaign to transform the department store ended abruptly when Ackman stepped down from the board due to a disagreement with fellow board members.
In 2011, Pershing Square began acquiring shares of Canadian Pacific Railway, eventually becoming the railway's largest shareholder. In November of that year, citing the company's poor financial performance, Ackman initiated a proxy contest with the goal of replacing CP's CEO and multiple board members. At the railway's annual meeting in May 2012, close to 90 percent of shareholder votes supported Ackman's dissident slate and much of the company's leadership was subsequently replaced. Following the successful proxy contest, The Globe and Mail's Report on Business Magazine named Ackman "CEO of the Year," stating that "no other CEO has had a bigger impact on how our publicly traded companies are steered than Ackman."
In January 2015, LCH Investments named Ackman one of the world's top 20 hedge fund managers after Pershing Square generated $4.5 billion in net gains for investors in 2014, bringing the fund's lifetime gains to $11.6 billion since its launch in 2004 through 2014.
On April 27, 2016, Ackman, along with Valeant Pharmaceuticals' outgoing Chief Executive Officer , J. Michael Pearson, and the company's former interim CEO, Howard Schiller, testified before the United States Senate Special Committee on Aging. The testifying panel answered questions related to the committee's concerns about repercussions to patients and the health care system posed by Valeant's business model and controversial pricing practices. Ackman sold his remaining 27.2 million share position in Valeant for about $300 million in March 2017 in what constituted a substantial loss. In 2017, Pershing Square paid $193.75 million to a group of Allergan shareholders as part of a $290 million settlement.
In 2016, Ackman began investing in Chipotle Mexican Grill, and the company was among Pershing Square's top holdings from 2017 to 2024. Ackman was credited with helping Chipotle rebound from years of losses by playing a part in hiring Brian Niccol as CEO in 2018.
In August 2017, Ackman acquired 8% of Automatic Data Processing (ADP) and launched a proxy fight to acquire 3 board seats. He lost the three-month proxy fight and exited the stock in 2019.
In 2021, Pershing Square acquired a 10 percent stake in Universal Music Group and, as of 2025, it is one of Pershing Square's largest positions. Prior to the initial investment, Ackman told Universal management that his grandfather, Herman Ackman, wrote a hit song in 1926 on Tin Pan Alley. It was later discovered that the song's recordings were owned by Universal, which then mounted and framed phonograph records and sheet music as a gift to Ackman. Ackman became a member of the company's board of directors in 2022, a position he retained until 2025.
In early 2024, Ackman aimed to raise capital to take a new fund known as Pershing Square USA public. However, after securing only $2 billion, he decided to withdraw the IPO on August 1, 2024. He announced plans to relaunch a version of the fund with a new transaction structure.
Ackman was chairman of Howard Hughes Holdings, one of Pershing's longest-held investments, from 2010 until 2024, when he stepped down from its board. In May 2025, Ackman rejoined the board as Executive Chairman after Pershing Square increased its investment in the company to 47%.
On August 8, 2026, Fortune reported that Bill Ackman's $35 billion hedge fund, Pershing Square Capital Management, maintains zero employee turnover among its 48 staff members. According to Ackman's interview on the Fortune Titans and Disruptors of Industry podcast, the firm maintains loyalty by offering multi-million dollar stock ownership to all employees—including janitors and receptionists—alongside extensive wellness perks and a unique two-month summer remote work policy.
In December 2012, Ackman announced that Pershing Square had made a $1 billion short bet against Herbalife, a maker of weight-loss and vitamin supplements, calling the company a "pyramid scheme".
A few months after Ackman's initial comments, billionaire investor Carl Icahn challenged Ackman's comment during a dual appearance by Ackman and Icahn on CNBC, during which both men insulted each other. Following this, Icahn announced a stake in Herbalife in January 2013. Over the following years, Icahn continued to buy Herbalife shares to combat Ackman's short.
Ackman's Pershing Square funded a persistent public relations campaign against Herbalife in an attempt to pressure state and federal regulators to investigate the company. He hired numerous lobbying firms, and had his team organize protests and letter writing campaigns. Ackman also paid organizations to help find victims of Herbalife, and personally lobbied Senator Linda Sánchez and the office of Senator Ed Markey, both of whom later sent letters to federal regulators. Following this campaign, the Federal Trade Commission initiated an investigation into Herbalife. Other regulators and law enforcement also got involved. In April 2014, Reuters reported that the FBI conducted a probe into Herbalife and reviewed documents obtained from the company's former distributors. On March 12, 2015, it was reported that federal prosecutors and the FBI were probing whether some people hired by Ackman made false statements in an attempt to encourage investigations and lower Herbalife's stock. Ackman was quoted that he would not back down from his claims against Herbalife. Neither Ackman nor Pershing Square were subpoenaed. The FBI probes into Herbalife and Ackman both failed to find sufficient evidence and were not pursued further.
In November 2017, Ackman said that he had covered his short-sell position, but would continue to bet against Herbalife using put options. On February 28, 2018, Ackman exited his near billion-dollar bet against Herbalife at a loss.
Ahead of the 2020 stock market crash, Ackman hedged Pershing Square's portfolio, investing $27 million to purchase credit protection, insuring the portfolio against steep market losses. Pershing Square first disclosed the hedge on March 3, 2020. According to Reuters, "Ackman said hedging was preferable to selling off his portfolio of companies whose businesses are otherwise strong." The hedge was effective, generating $2.6 billion in less than one month.
On March 18, 2020, in a phone interview with CNBC, Ackman called upon President Donald Trump for a "30-day shutdown" of the American economy to slow the spread of coronavirus and minimize loss of life and ensuing economic destruction resulting from the shutdown. Ackman warned that without intervention, hotel stocks were "going to zero" and said that America could "end as we know it". He also cautioned U.S. companies to stop stock buyback programs because "hell is coming".
Ackman later received criticism for actively buying discounted equity stakes in the very companies he was warning could fail; however, Ackman already had realized roughly half of the gains before appearing during the CNBC interview.
In a November 2020 interview, Ackman said that he had grown concerned about COVID-19 because he had seen the film Contagion.
