Colleen M. O’Neil (Calfee, Halter & Griswold LLP) – Cleveland, OH

High-Stakes Business Litigation and Advocacy

Colleen M. O’Neil is a formidable trial attorney and Co-Chair of the Litigation Practice Group at Calfee, Halter & Griswold LLP, one of Cleveland’s most storied and prestigious law firms. Based in the historic Calfee Building on East 6th Street, Colleen O’Neil has established herself as a go-to litigator for complex commercial disputes. With over two decades of experience, she represents a broad spectrum of clients, from Fortune 500 corporations to financial institutions and high-net-worth individuals. Her practice is defined by a relentless pursuit of her clients’ business goals, whether that means aggressively prosecuting a trade secret claim in federal court or strategically defending a company against shareholder disputes.

As a leader within the firm, Colleen O’Neil brings a depth of expertise in Commercial Litigation that is unmatched. She has successfully handled cases involving breach of contract, business torts, and employment matters across the nation. Her specific focus on Probate and Estate Litigation also makes her a critical resource for families and trustees navigating the complexities of contested wills and trust administration. Colleen is known for her practical, results-oriented approach; she understands that litigation is a business tool and works to resolve conflicts efficiently while maximizing value for her clients. Her reputation for excellence has earned her consistent recognition in Chambers USA and Best Lawyers in America.

Legal Specializations

• Commercial Litigation: Handling complex contract disputes, business torts, and partnership breakups in state and federal courts.
• Trade Secret Litigation: protecting intellectual property and sensitive business information from misappropriation by competitors or former employees.
• Probate Litigation: Representing fiduciaries and beneficiaries in disputes over will contests, trust interpretations, and allegations of breach of fiduciary duty.
• Employment Defense: Defending employers against Title VII claims, discrimination lawsuits, and enforcement of non-compete agreements.
• Real Estate Disputes: Litigating issues related to property development, commercial leases, and zoning challenges.

Recognized for Excellence

Colleen M. O’Neil’s standing in the legal community is a testament to her skill and dedication. She has been named a Super Lawyer for over a decade and is listed among the "Top 50 Women Attorneys in Ohio." Beyond her client work, she is a pillar of the Cleveland legal community, serving on the Board of Visitors for the Cleveland State University College of Law and as a founding member of the Irish American Law Society of Cleveland. Operating from Calfee’s headquarters-a fully restored historic landmark that symbolizes the firm’s commitment to the city-Colleen O’Neil continues to set the standard for high-caliber litigation services in Northeast Ohio.