Cassidy O’Sullivan practices complex commercial litigation, managing all aspects of a case for a variety of clients.
Prior to joining Hueston Hennigan, Ms. O’Sullivan was an associate at Herbert Smith Freehills in Sydney, Australia where she represented international clients in a variety of commercial disputes, including shareholder disputes, corporate takeover litigation, regulatory investigations and inquiries, business torts, contract disputes, and international arbitration.
During law school, Ms. O’Sullivan served as a research assistant for Prof. Barry Friedman and the American Law Institute. She was also an extern for the Public Integrity Bureau of the Kings County (Brooklyn) District Attorney’s Office, and received the George Colin Award for distinction in the Traditional LL.M. at graduation.
Ms. O’Sullivan has also worked as a teaching assistant and grader in Constitutional Law at the University of Sydney Law School, and previously interned at the Australian Law Reform Commission, Australia’s peak law reform body, and at the Innocence Project at the University of Sydney (Not Guilty: The Sydney Exoneration Project).
Experience
Obtained a complete defense victory for Tri Star Sports & Entertainment Group on copyright infringement claims. Prior to the motion to dismiss stage, the plaintiff voluntarily dismissed both claims after Tri Star filed a letter detailing deficiencies in the plaintiff’s claims.
Successfully defended Amazon.com and three Amazon executives against a historic FTC lawsuit targeting its Prime membership. Described as “a win for Amazon,” the case settled after three days of trial with no admissions of liability. (See “Why Amazon actually got off easy despite ‘historic’ $2.5 billion Prime deceptive practices settlement,” Fortune; “Why $2.5B Might Not Be Enough In FTC’s Amazon Settlement,” Law360).
Successfully settled a breach of contract dispute for a national law firm arising from a commercial leasing representation agreement.
Successfully settled an employment dispute for a large biotechnology company relating to executive compensation worth millions of dollars.
Successfully settled a suit brought by a group of investors of an acquired start-up against a public biotechnology company alleging breach of contract, fraud, and conversion.
Obtained a highly favorable settlement in advance of trial for two California agencies against claims of trade secret misappropriation and breach of contract arising out of a project to develop and implement California’s online health insurance exchange.
Defended a billion-dollar apartment/hotel company in litigation arising out of a commercial leasehold impacted by the COVID-19 pandemic.
Advised Monster Energy Company in connection with a Chapter 11 bankruptcy filing by rival beverage company Vital Pharmaceuticals, Inc. and Monster’s resulting acquisition of Vital.
Successfully settled a suit brought by Don Lee Farms against Beyond Meat alleging breach of contract, fraud, and negligent misrepresentation arising out of Beyond Meat’s termination of an exclusive supply agreement; and defended against Beyond Meat’s related cross-claims alleging breach of contract, misappropriation of trade secrets, trademark infringement, and fraud.
Successfully settled a class action lawsuit filed against Ring (an Amazon.com subsidiary) arising out of alleged hacking of Ring devices.
Successfully settled a suit brought by Palantir Technologies against a former early investor alleging breach of contract, misappropriation of trade secrets, and other wrongful conduct after defeating a motion for summary judgment.
Representing AbbVie, a defendant in the multibillion-dollar Allergan textured breast implant litigation, which involves approximately 1,700 individual lawsuits and a nationwide class action in four venues including multidistrict litigation in the District of New Jersey. The plaintiffs contend AbbVie’s BIOCELL® textured breast implants cause a rare type of cancer, and they argue AbbVie is liable under manufacturing defect, failure to warn, and misrepresentation theories.
Representing Amazon in a copyright infringement action brought by a t-shirt design company asserting direct, vicarious, and contributory liability claims arising from designs offered through Amazon’s print-on-demand service, Merch by Amazon.
Representing six plaintiffs pro bono in a putative class action against private prison and immigration detention center operator The GEO Group, Inc. and Spartan Chemical Company, Inc. alleging that GEO repeatedly sprayed detainees at the Adelanto Detention Center with a toxic pesticide at high concentration levels while they were imprisoned at the facility during the COVID-19 pandemic.
Representing a global online retailer in pre-litigation investigations relating to a patent infringement dispute.
Representing an individual plaintiff pro bono in a federal civil rights action brought against two law enforcement offices in Louisiana arising out of an unlawful police stop, search, and arrest with the Social Justice Legal Foundation and the ACLU of Louisiana.
Favorable settlement obtained for the The Carlyle Group against $120M claims in early stages of trial of takeover dispute.
Defended Pemba Capital against shareholder claims in expedited four-week trial concerning $200M takeover.
Advised U.S. investment bank on $1B potential exposure for inadvertent non-reporting pursuant to finance laws.
Advised a multinational contractor on potential claims under laws of Australia, Spain, UAE, and Singapore for precontractual representations.
Advised a multinational petroleum company on possible global exposure to securities class actions in the event of a catastrophic failure.
Represented a major energy provider in enforcement proceedings commenced by the Australian Energy Regulator against windfarm operators after a catastrophic 2016 state-wide black out.
Provided strategic advice to a state government seeking to terminate a significant supplier contract.
Secured substantial recognition payments for nine young survivors of domestic and sexual violence under a statutory victims’ assistance scheme.
Recognitions
- Best Lawyers: Ones to Watch in America (2026)