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Daniel Leff

Counsel
Counsel
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Areas of Focus

Overview

Daniel Leff is an antitrust litigator, trial lawyer, and strategic advisor. As a former state assistant attorney general, he draws on his experience litigating complex, high-profile antitrust cases for clients involved in or anticipating litigation as both plaintiffs and defendants. Dan also counsels and advocates for companies seeking antitrust regulatory approval for mergers, acquisitions, and innovative business deals.

Dan joined Crowell from the Massachusetts Attorney General's Office (AGO), where he served in the Office's Antitrust Division. In that role, he worked hand-in-hand with enforcers from the U.S. Department of Justice (DOJ), the Federal Trade Commission (FTC), and the attorney general offices of nearly every U.S. state and territory to investigate and litigate merger, monopolization, and cartel matters.

His work with the AGO included successfully trying merger and Sherman Act § 1 cases in federal court. He was also a lead member of a plaintiff group comprising nearly every state attorney general office in the country in a large pharmaceutical price-fixing multidistrict litigation (MDL).

Dan also investigated, litigated, and settled numerous competition matters in industries including telecommunications, transportation, energy, agricultural products, healthcare, and pharmaceuticals. Clients benefit from Dan's experience in the Sherman, Clayton, and FTC acts and numerous state antitrust and consumer protection statutes, as well as his familiarity with the perspectives of state and federal enforcers across the country.

Dan began his career at Crowell, where he represented clients facing federal and state antitrust, consumer protection, and environmental scrutiny, primarily in the telecommunications and energy industries. He also previously worked for an international law firm in Boston, representing pharmaceutical and medical device companies facing federal civil and criminal investigations.

Career & Education

    • Massachusetts
      Commonwealth of Massachusetts Office of the Attorney General, Antitrust Division, Assistant Attorney General, 2019–2024
    • Massachusetts
      Commonwealth of Massachusetts Office of the Attorney General, Antitrust Division, Assistant Attorney General, 2019–2024

    • New York University School of Law, J.D., 2013
    • Georgetown University School of Foreign Service, B.S.F.S., 2005
    • New York University School of Law, J.D., 2013
    • Georgetown University School of Foreign Service, B.S.F.S., 2005

    • District of Columbia
    • New York
    • Massachusetts
    • U.S. Court of Appeals for the First Circuit
    • U.S. District Court for the District of Columbia
    • District of Columbia
    • New York
    • Massachusetts
    • U.S. Court of Appeals for the First Circuit
    • U.S. District Court for the District of Columbia

Daniel's Insights

Client Alert | 5 min read | 10.13.26

New York-Presbyterian Hospital Ruling Signals Widening Antitrust Exposure for Hospital Contracting Practices

On October 1, 2026, Judge Brian M. Cogan of the U.S. District Court for the Eastern District of New York denied NYP’s motion to dismiss a consolidated antitrust complaint brought by three self-funded union health plans. The ruling is significant for two reasons. First, it demonstrates that plaintiffs can successfully allege market power against hospital systems even in the absence of traditionally high market shares. Second, the court’s reasoning closely tracks the arguments advanced by the DOJ in its Statement of Interest filed in the case: that market power need not be established through market share alone and can be shown through direct evidence such as supracompetitive pricing, and that exclusionary conduct and rival foreclosure are not required elements of a Section 1 claim. The recent decision validates the government’s legal theories and could enhance the viability of the DOJ’s parallel action against NYP, which is currently proceeding in the Southern District of New York....

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Representative Matters

Litigation and Investigations

  • Representing several health plans seeking to recover damages in pharmaceutical pay-for-delay and price-fixing litigation.
  • Defending a major managed care company in an Affordable Care Act discrimination class action litigation.
  • Securing a large settlement for major health plans in pharmaceutical product-hopping antitrust and fraud litigation.
  • Representing a major pharmaceutical and medical device manufacturer facing U.S. Attorney’s Office False Claims Act and Anti-Kickback Statute investigations.

Merger Clearance

  • Representing DIRECTV as antitrust counsel in its proposed acquisition of the DISH video distribution business from EchoStar, including leading the merger review process before DOJ and providing strategic counsel and advice in connection with the transaction.
  • Representing TransCanada in its $13 billion acquisition of Columbia Pipeline Group.
  • Representing United Technologies in its sale of Sikorsky to Lockheed Martin.
  • Representing AT&T Inc. in its acquisition of DIRECTV.

Government Experience

  • Securing an injunction blocking a major airline joint venture at trial.
  • Securing an injunction blocking an airline merger at trial.
  • Representing Massachusetts in multi-district litigation over pharmaceutical price fixing.
  • Representing Massachusetts in challenging T-Mobile’s acquisition of Sprint.

Daniel's Insights

Client Alert | 5 min read | 10.13.26

New York-Presbyterian Hospital Ruling Signals Widening Antitrust Exposure for Hospital Contracting Practices

On October 1, 2026, Judge Brian M. Cogan of the U.S. District Court for the Eastern District of New York denied NYP’s motion to dismiss a consolidated antitrust complaint brought by three self-funded union health plans. The ruling is significant for two reasons. First, it demonstrates that plaintiffs can successfully allege market power against hospital systems even in the absence of traditionally high market shares. Second, the court’s reasoning closely tracks the arguments advanced by the DOJ in its Statement of Interest filed in the case: that market power need not be established through market share alone and can be shown through direct evidence such as supracompetitive pricing, and that exclusionary conduct and rival foreclosure are not required elements of a Section 1 claim. The recent decision validates the government’s legal theories and could enhance the viability of the DOJ’s parallel action against NYP, which is currently proceeding in the Southern District of New York....

View All Insights

Insights

Client Alert | 5 min read | 10.13.26

New York-Presbyterian Hospital Ruling Signals Widening Antitrust Exposure for Hospital Contracting Practices

Webinar | 10.07.26

The Future of State Enforcement: Insights from the 2026 AG Elections | Part One: Mid-Cycle Check-In: The AG Races to Watch

Speaking Engagement | 10.07.26

"The Future of State Enforcement: Insights from the 2026 AG Elections | Part One: Mid-Cycle Check-In: The AG Races to Watch," Crowell & Moring Webinar.

Blog Post | 09.22.26

Register Now! The Future of State Enforcement: Insights from the 2026 AG Elections

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Practices

Industries

Daniel's Insights

Client Alert | 5 min read | 10.13.26

New York-Presbyterian Hospital Ruling Signals Widening Antitrust Exposure for Hospital Contracting Practices

On October 1, 2026, Judge Brian M. Cogan of the U.S. District Court for the Eastern District of New York denied NYP’s motion to dismiss a consolidated antitrust complaint brought by three self-funded union health plans. The ruling is significant for two reasons. First, it demonstrates that plaintiffs can successfully allege market power against hospital systems even in the absence of traditionally high market shares. Second, the court’s reasoning closely tracks the arguments advanced by the DOJ in its Statement of Interest filed in the case: that market power need not be established through market share alone and can be shown through direct evidence such as supracompetitive pricing, and that exclusionary conduct and rival foreclosure are not required elements of a Section 1 claim. The recent decision validates the government’s legal theories and could enhance the viability of the DOJ’s parallel action against NYP, which is currently proceeding in the Southern District of New York....

View All Insights