Diane P. Sullivan

Partner Princeton, New York


Diane P. Sullivan
Diane P. Sullivan is a partner in the Litigation Department in Weil’s New York, NY and Princeton, NJ offices where she specializes in trial of high stakes cases across practice areas. She also serves on the Firm’s Management Committee.

Diane is a nationally recognized trial attorney. In 2012, The American Lawyer featured her in its “Litigator of the Year” edition, noting that she “isn’t a hired gun; she’s more like a hired bazooka repeatedly parachuting into high-stakes cases leading up to trial and securing victories.” In three different years, 2007, 2017 and 2019, The National Law Journal featured her jury verdicts in its annual series: “Winning: Successful Strategies from the Nation’s Top Litigators” which highlights significant trial wins by the nation’s top trial lawyers. The same publication highlighted her jury verdicts as among the “Top Verdicts of the Year” in seven different years. In 2021, Chambers USA ranked her in the “Star” category as one of the top five trial lawyers in the country. Clients noted “she is a fantastic and fearless trial lawyer at the top of her game.” “She is a visionary, very bold and proactive, focusing on delivering for her clients.” “A consummate trial lawyer – there is nobody more focused on the jury than Diane.” “She has a mastery of the courtroom.” Chambers also described her as “a trial powerhouse” and “a renowned courtroom presence, equally adept at handling the full range of complex commercial cases, mass torts and class actions.” Clients noted she is an “absolutely sterling, extraordinary trial lawyer,” “fantastic,” “a top choice in bet-the-company litigation,” and “one of the best I’ve ever seen.” Clients stated: “She controls a courtroom and is scared of nothing and no one.” Clients further advised: “She is a first class trial lawyer in every way,” “a natural on her feet,” “a real weapon at trial,” and “one of the best trial lawyers in the country.” “She is one of the best trial lawyers out there; we go to her with our most important work.” With experience across a range of industries, she is praised as “a truly tremendous trial lawyer” and “a superstar litigator” who “keeps on winning ‘nationally significant cases’ in jurisdictions throughout the country.” Clients remarked: “Her trial presence is unmatchable,” and “she was just wonderful – a powerful presence who boils down complex issues in a way that can be readily communicated to a jury.” Chambers also stated: “She’s rightly named a top lawyer – she handles some of the toughest cases.” Clients praised her “remarkable talent,” “amazing cross-examinations,” and “fantastic ability to build up a narrative and connect with juries in an honest way.” They also noted that she “gets great results” and is “fearless, excellent, and as zealous an advocate as there is in the Bar.” “She comes out punching from start to finish.”

In 2017, she was one of 19 attorneys in the country named a “Lawdragon Legend” for being recognized as one of the 500 Leading Lawyers in America for ten years or more – now 14 years as of the 2021 edition. Lawdragon noted “she has produced a batting average in jury trials in the Hall of Fame category” and described her as “one of the most feared trial lawyers in the nation.” The publication further stated: “In courts or arbitrations for corporate clients, she is as good as any advocate in the country.” Diane was named one of Law360’s 2015 “Trial Aces” in its inaugural list recognizing the top trial attorneys in the country based on success in high-stakes trials, and as one of Law360’s 2016 Trial “MVPs” in the publication’s inaugural ranking of the five most valuable trial lawyers in the country based on significant trial victories. Diane was also selected as one of Law360’s Litigation “MVPs” for success in major litigation and has been repeatedly recognized as a Law360 “Legal Lion” for success in high profile litigations. In 2010, Diane was also named by Law360 as one of the most admired attorneys in the nation based on a survey of her peers and in-house counsel. A member of The Legal 500 “Hall of Fame” for lawyers at “the pinnacle of the profession,” the publication noted that she is “an absolute star,” “a terrific trial lawyer,” “tough and fearless,” “a gifted trial lawyer in ‘big ticket, bet-the-company trials’ who regularly secures favorable verdicts in high-stakes matters.” She is rated by clients as “just a brilliant, brilliant trial lawyer” and appreciated because “she wins her cases.” She is “in a small class of bet-the-company trial lawyers.” In 2018, Benchmark Litigation described her as “one of the nation's most iconic trial lawyers” and in 2019 she received the prestigious Benchmark Litigation “Hall of Fame” award and is listed on Benchmark’s 2020 and 2021 Top 100 Trial Lawyers list.

She has been featured for her trial victories on the front pages of The New York Times, The Wall Street Journal and on the cover of The American Lawyer, among other publications. Diane has also been recognized by Lawyers Weekly USA, which named her one of the top 10 lawyers of the year, noting her trial performance “electrified the courtroom.” In 2018, Diane was included in the Financial Times’ top 100 female champions in its “HERoes: Champions of Women in Business” ranking. The International Who’s Who references Diane for commendation by her peers as one of the most highly regarded practitioners in the field. She has repeatedly been named for inclusion in Best Lawyers in America, including 2018 “Lawyer of the Year” in the areas of Bet-the-Company litigation, Commercial Litigation, and representing defendants in Mass Tort/Class Action Litigation. In 2017, Diane received the Euromoney Women in Business “Most Outstanding Practitioner” award, given to one lawyer each year for her contributions to the legal profession. In 2012, Diane was named one of the top 15 Female Trial Attorneys by Law360 for scoring “landmark victories” and “blazing trails.” She has been consistently recognized by Benchmark Litigation as a “Litigation Star” and as one of the Top Ten Women Litigators in the country. Since 2016, LMG Life Sciences Guide has recognized Diane as a “Life Science Star” and praised her as a “nationally revered trial lawyer who has routinely secured victories, often high stakes and precedent-setting, for a ‘Who’s Who’ list of clients.” In 2019, LMG also awarded her “Trial Lawyer of the Year,” “Impact Case of the Year,” and “Product Liability Attorney of the Year” honors at its annual Life Sciences Awards. In 2021, Courtroom View Network listed her among the most effective trial lawyers doing civil jury trial work in its video edition featuring 10 “Powerhouse Trial Pros.”

Among Diane’s notable trial victories and representations are:

  • Lead trial counsel for pharmacy chain defendant in the first bellwether jury trial against pharmacies in the massive MDL opioid litigation where two plaintiff Ohio counties sought 3 billion dollars in damages. Secured a successful settlement of all pending cases against our client at close of plaintiffs case.
  • Lead trial counsel for Johnson & Johnson securing a unanimous defense verdict following a four-week bellwether jury trial in New Jersey state court involving claims J&J’s baby powder caused cancer. This was the first defense verdict in New Jersey courts, where thousands of cases in the talc mass tort are pending against the Company. The verdict, described as a “slam dunk” for the defense, helped to “turn the tide” in the litigation, according to Reuters and The American Lawyer, which featured the verdict in its “Litigator of the Week” series. Law360 also highlighted the win as a landmark victory of 2018. Courtroom View Network showcased the win as the most impressive defense verdict of the year.
  • Lead trial counsel for GE securing a complete defense win after a four-week arbitration in a suit involving claims for over $1 billion in damages relating to construction of a clean energy power plant.
  • Lead trial counsel for ESPN securing a defense verdict against Dish Network following a three-week jury trial in the Southern District of New York involving more than $150 million in claims. This victory was featured in The American Lawyer and in Law360’s “How They Won It” series.
  • Lead trial counsel for Merck in the legal battle over Vioxx®. Diane secured the first trial victory for Merck, convincing jurors to reject the plaintiff’s failure to warn and consumer fraud claims. This defense verdict, in a plaintiff-friendly “judicial hell-hole” jurisdiction, was featured on the front pages of newspapers across the country and InsideCounsel named it one of the “five verdicts of 2005 that are reshaping corporate defense strategies.” The National Law Journal featured the win as one of the top verdicts of the year. Subsequently, Diane scored another victory for Merck in the Vioxx® litigation – the first defense verdict in a long-term use case. The victory was hailed by analysts as significant, particularly in serving to thwart future collateral estoppel arguments. This verdict was also featured by The National Law Journal as one of the top verdicts of the year. She went on to win yet a third jury verdict for Merck in a Vioxx® case; a victory also featured in legal and lay publications.
  • Lead trial counsel for Philip Morris USA securing a unanimous defense verdict following a three-week class action jury trial of medical monitoring claims pursued on behalf of all Massachusetts smokers of Marlboro cigarettes who had smoked for 20-plus pack-years, with a total class size in the tens of thousands. This verdict was featured in The American Lawyer “Litigator of the Week” series, in Law360, and in The National Law Journal “Winning” series as a top verdict of the year.
  • Lead trial counsel for global energy company Repsol in environmental litigation involving claims of “alter ego” and fraudulent conveyance. The Weil team secured a victory on all claims involving over $1 billion dollars in damages while also succeeding on Repsol’s $65 million counterclaim. The win was profiled in Law360.
  • Lead trial counsel for Philip Morris USA securing a defense verdict after a four-month jury trial in St. Louis where 37 Missouri hospitals sued for over $500 million dollars in economic loss plus punitive damages relating to costs for treating patients with smoking-related illness. The victory was described by the press as “resounding and complete.” Diane’s work in this trial was highlighted by the Financial Times as an example of “innovative lawyering” and was also recognized by The American Lawyer in its “Litigator of the Week” profile.
  • Lead trial counsel for Procter & Gamble in class action litigation relating to its probiotic supplement Align® securing a favorable settlement on the eve of trial.
  • Lead trial counsel for SAC Capital and Steven Cohen in litigation brought by Fairfax Financial Holdings for $8 billion dollars alleging fraud and conspiracy relating to short sales of securities; summary judgment granted for Mr. Cohen and for SAC Capital before trial. The win was highlighted in newspapers across the country and featured in Law360.
  • Lead trial counsel for Walgreens in consumer class action litigation relating to Theranos Labs blood testing technology, securing dismissal of core claims against Walgreens and an indemnification from Theranos.
  • Lead trial counsel for a major office supply company in $6 billion dollar antitrust trial.
  • Lead counsel for Sanofi securing a dismissal of all claims in Illinois federal court in a putative consumer class action following Sanofi’s global recall of its epinephrine injection product, Auvi-Q®. The win was featured in Law360.
  • Lead counsel for defendant in the Lac-Mégantic train derailment involving environmental, property and wrongful death claims in multiple forums securing a favorable settlement and a channeling injunction preventing future claims.
  • Lead trial counsel for AstraZeneca securing a defense verdict in the first bellwether trial of more than 20,000 claims involving the prescription drug Seroquel®. The verdict was described by the press as a “huge win” for AstraZeneca, particularly the jury’s finding that AstraZeneca’s warnings were adequate. The trial victory led to a global settlement of all claims.
  • Lead trial counsel for Cardinal Health Corporation in patent infringement litigation relating to gel capsule technology. Secured favorable settlement on eve of trial.
  • Lead trial counsel for Merck and Schering-Plough in class action lawsuits alleging consumer fraud and RICO claims relating to the drugs Vytorin® and Zetia®; favorably settled before trial.
  • Lead trial counsel for a major Japanese manufacturer in federal False Claims Act suits involving hundreds of millions of dollars in potential damages; secured favorable settlement on eve of trial.
  • Lead trial counsel for Baxter Healthcare Corporation and Allegiance Healthcare Corporation in the first trial in the federal MDL latex medical device mass tort litigation, which resulted in a defense jury verdict. The verdict was named one of the top defense verdicts of the year by The National Law Journal.
  • Lead trial counsel for Nutraquest in the ephedra mass tort litigation, including defending a $685 million personal injury claim filed by the estate of professional baseball player Steve Bechler. Secured favorable global settlement on eve of trial.

Diane also has an active pro bono practice. In February 2020 she negotiated a groundbreaking settlement with the New York City Housing Authority (NYCHA) in a class action lawsuit she commenced on behalf of domestic violence survivors challenging NYCHA’s administration of housing assistance in the wake of domestic abuse. The settlement, reported in Politico and other publications, remedies a system that deprived survivors’ due process rights and placed them in danger of eviction. As a result of Diane’s advocacy, domestic violence survivors now have the means of obtaining new housing vouchers in their names, safeguarding them against the loss of their homes.

Diane is a frequent author and speaker on topics relating to litigation and trial practice.

Awards and Recognition, Latest Thinking, Firm News & Announcements

Awards and Recognition

View all

Latest Thinking

Firm News & Announcements

View all