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Photo of William O'Neil   William O'Neil, Esq.
Winston & Strawn LLP
Chicago, IL

Bill O’Neil is an accomplished trial lawyer who concentrates his practice on a variety of business disputes.

A significant portion of Bill's practice involves representing private equity funds and their portfolio companies. Bill frequently represents buyers and sellers in post-closing disputes, including working capital, representation and warranty, and fraud claims. Bill also represents buyers in claims against representation and warranty insurance carriers. More than a dozen private equity funds have retained Bill to handle these disputes; often where another law firm handled the underlying transaction. He brings a practical, business-minded approach to contentious disputes; he is frequently praised by his clients for the depth of his understanding of M&A transactions.    


Bill also represents numerous public company clients in corporate governance litigation, shareholder strike suits, internal investigations, and other complex business litigation. He has represented dozens of Fortune 500 companies in disputes ranging from routine to high-stakes, “bet the company” litigation. Mr. O’Neil is also frequently called upon to provide risk management and litigation avoidance advice to his clients.

Bill has significant antitrust experience. He was defense counsel in In re Automotive Parts Litigation, In re Linerboard Antitrust Litigation, and In re Sulfuric Acid Litigation, and successfully prosecuted price-fixing claims on behalf of Solyndra LLC against three of China’s largest solar panel manufacturers.

Bill’s pro bono cases have included representing a prison inmate in a successful appeal before the Seventh Circuit Court of Appeals that resulted in new law in the circuit, the court’s reversal of its own prior precedent, and the reversal of the defendant’s conviction.

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