Atty. William B. Mack
William B. Mack is a co-chair of the Financial Regulatory & Compliance Practice.
Financial Regulatory & Compliance & More Attorney · Serving New York, NY · 22+ Years Experience
Profile Summary
About William B. Mack at a Glance
William B. Mack is a Shareholder based in New York, New York, practicing at Greenberg Traurig, LLP. They have 22+ years of legal experience, licensed to practice since 2004. Their practice focuses on business and government. Admitted to practice in New York U.S. District Court for the Eastern District of New York U.S. District Court for the Southe (2004). Educated at State University of New York at Albany (B.A., 2000) and Columbia Law School J.D. 2003 Writing and Research Editor Columbia Law School J.D. Columbia Journal of Law and Social Problems (—). Active member of Professional & Community Involvement •Member, Chamber of Digital Commerce Task Force on Crypto Asset Trading Platforms •Term Member, Council on Foreign Relations •Board of Directors, Hebrew Language Academy. Serves clients in New York, NY and the surrounding metropolitan area.
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About William B. Mack
- William B. Mack is a co-chair of the Financial Regulatory & Compliance Practice
- He is experienced in advising companies on regulatory and compliance matters relating to the Securities and Exchange Commission regulations, the Exchange Act, Anti-Money Laundering laws and Financial Industry Regulatory Authority (FINRA) rules
- William’s practice involves all aspects of broker-dealer regulation, including Self-Regulatory Organization (SRO) membership, supervision, employment, research, soft dollar arrangements, chaperoning of foreign broker-dealers, social media, use of foreign finders, anti-money laundering rules, alternative trading systems (ATS), exchanges, and market making issues
- He also provides regulatory guidance to investment banking clients in connection with securities offerings and related trading issues
- William advises firms in the FINRA new membership (NMA) and the continuing membership (CMA) processes
- William assists firms to develop or amend their written supervisory procedures and compliance manuals
- William routinely represents clients who are negotiating placement agent agreements, foreign finders agreements, clearing agreements, agreements with registered representatives and expense-sharing agreements
- William assists broker-dealers and their associated persons to respond to regulatory examinations and inquiries and provides effective representation in a range of enforcement proceedings with the SEC, FINRA, NYSE, state and foreign regulatory authorities
- He regularly prepares and defends witnesses in FINRA on-the-record interviews and SEC testimony
- Enforcement matters have involved issues including market manipulation, supervision, customer defalcations, insider trading, anti-money laundering, distribution of unregistered securities, direct market access, market making, soft dollar arrangements, cross border trading, electronic intrusion and customer impersonation, sales practices, supervision, private placements, ETFs, indexes, and other securities products
- William regularly addresses questions with respect to what activities require or are exempt from broker-dealer registration
- William assists firms in obtaining guidance, interpretive letters, and no-action relief from FINRA and the SEC with respect to novel securities issues and the creation of new products and services
- William also advises clients on cryptocurrency, tokenization, NFTs, DeFi structures, and digital asset exchanges and trading
- Prior to joining the firm, William was a Principal Counsel for Enforcement at FINRA
- Before FINRA, he was the Director of the Executive Secretariat in the Office of the U.S
- Trade Representative
- William also served as a Deputy Associate Counsel at the White House, advising primarily on appointments and investigations
- Before the White House, he practiced at large firms in New York
- William clerked for Judge Robert L. Carter in the Southern District of New York
- Judicial Clerkships •Hon
- Robert L. Carter, U.S
- District Court for the Southern District of New York Recognition & Leadership Awards & Accolades •Listed, The Legal 500 United States, •Finance - Financial Services Regulation, 'Recommended Lawyer,' 2023-2024 •Finance - Fintech, 'Recommended Lawyer,' 2024 •Team Member, City & State, 'Top 50 NYC Lobbyists,' 2021 •Listed, The Legal 500 United States, Fintech, 2020 •Team Member, Best Lawyers in America 'Top Listed - Government Relations,' 2018 •Recipient, University at Albany Alumni Association, 'Excellence in Public Service Award,' 2018 •Listed, City & State’s 'New York City 40 under 40 Rising Stars,' 2015
Practice Areas Explained
William B. Mack's Areas of Legal Practice
Each practice area below reflects the types of cases William B. Mack handles, with a practical overview of what that area of law involves and how it may apply to your situation in New York.
Business & Corporate Law in New York
Business attorneys advise founders and growing companies on entity formation, contracts, financing, M&A, and dispute resolution.
William B. Mack is one of 497,491 business attorneys indexed nationally. Browse business attorneys in New York →
Government & Administrative Law in New York
Attorneys for administrative law, agency hearings, government contracts, licensing, and public benefits.
William B. Mack is one of 131,162 government attorneys indexed nationally. Browse government attorneys in New York →
Jurisdictional Context
Why Local Counsel Matters in New York
Practicing law in New York. Legal matters in New York are governed by state-specific rules of civil and criminal procedure, statutes of limitations, and substantive law. Cases originating in New York are typically filed in the local municipal court or the appropriate New York state district court, depending on subject matter and amount in controversy. An attorney licensed in New York brings working knowledge of local procedural deadlines, judicial practices in this venue, and the substantive law that applies to cases brought here. Out-of-state attorneys generally cannot represent clients in New York courts without local counsel or pro hac vice admission.
New York Courts and Legal Process
Choosing a New York-based attorney means your counsel already knows the local docketing timelines, preferred filing formats, and how individual judges typically rule on procedural motions — details that only come from practicing in this jurisdiction day after day. That local familiarity can translate to better strategy, faster filings, and fewer costly surprises.
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Professional Profile
Why Clients in New York Choose William B. Mack
Selecting an attorney is one of the most consequential decisions you can make when a legal matter arises. Below are the core qualities that distinguish William B. Mack's practice in the field of business and government.
Decade-Tested Legal Experience
William B. Mack brings 22+ years of hands-on legal practice — enough to have navigated the recurring fact patterns, procedural traps, and negotiation dynamics that shape case outcomes.
Broad Practice Area Coverage
Covering business and government, William B. Mack can address the full spectrum of a client's legal needs without requiring referrals to separate specialists for each issue.
Local Presence in New York
A New York-based practice means William B. Mack attends hearings in the same courthouses, knows the local clerks, and understands the unwritten scheduling norms that affect every case filed here.
Case Types
Common Legal Issues William B. Mack Handles in New York
Below is a representative sample of the types of matters William B. Mack has experience with under New York law. If your situation involves one of these case categories, this attorney may be well positioned to help you understand your options.
This list is illustrative, not exhaustive. Contact William B. Mack directly to discuss the specifics of your situation.
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William B. Mack's Practice Areas & Specializations
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