Andrew J. Sioson

ANDREW SIOSON counsels broker-dealers, crypto and digital asset companies, exchanges, trading platforms and other financial institutions on regulatory, transactional, and enforcement matters. His practice spans the full lifecycle of regulated businesses – from structuring new products and business models and obtaining regulatory approvals to navigating examinations, investigations, and enforcement matters. He is recognized by Chambers FinTech for USA Nationwide FinTech Legal: Blockchain & Cryptocurrencies (2025–2026) and by Best Lawyers: Ones to Watch^® in America for Securities Regulation (2026).

Andrew counsels clients before the U.S. Securities and Exchange Commission (SEC), Financial Industry Regulatory Authority (FINRA), Federal Reserve Board (FRB), Public Company Accounting Oversight Board (PCAOB), and other state and federal regulators. He regularly advises on securities market structure, broker-dealer regulation, and trading platforms, tokenized securities and other digital assets, blockchain and distributed ledger technology, and artificial intelligence.

“His expertise and depth in understanding of the underlying rationale for regulations allows him to think creatively and navigate grey areas of the law.”
Chambers USA 2026

Andrew advises clients on complex securities regulatory matters and represents them in high-stakes examinations, investigations, and enforcement matters. His regulatory practice includes counseling broker-dealers and other market participants on SEC and FINRA requirements; structuring and launching new products and regulated businesses; establishing and operating alternative trading systems, clearing agencies, transfer agents, and national securities exchanges; and obtaining regulatory approvals. His enforcement practice draws on that regulatory foundation to represent clients before the SEC, FINRA, and other regulators, allowing him to anticipate risk when advising on new business models and bring a deep understanding of the underlying framework when defending clients under scrutiny.

Prior to joining Sidley, Andrew served as special counsel in the SEC’s Division of Trading and Markets, where he supervised equities and options exchanges, alternative trading systems (ATSs), broker-dealers, and other key securities market participants. His work included SEC rulemakings involving order handling disclosures, market structure reform, self-regulatory organization (SRO) rule changes, market data and National Market System (NMS) plan governance, exchange-traded fund (ETF) listing standards, and Dodd-Frank Act implementation. Before joining the SEC, Andrew practiced corporate law in New York, focusing on private funds, finance, and mergers and acquisitions.

Andrew is also a registered certified public accountant (CPA) and has held a Series 7 license. His financial background, regulatory experience, and private-practice work give him a practical understanding of how financial institutions operate and help him bridge business objectives and regulatory requirements.

Andrew’s financial services and digital asset practice includes:

• Advising broker-dealers on a variety of regulatory and enforcement issues, involving Reg. NMS, Reg. SCI, Reg. SHO, Reg ATS, Reg T, the Market Access Rule (Rule 15c3-5), the Market Data Infrastructure Rules, the Customer Protection Rule (Rule 15c3-3), best execution obligations, stock-lending, recordkeeping rules, and cross-border registration requirements.
• Representing broker-dealers in negotiating clearing, prime brokerage, securities lending, and other agreements related to broker-dealer operations.
• Advising market participants on establishing and operating ATSs, clearing agencies, transfer agents, and national securities exchanges — including those facilitating the trading of traditional securities and tokenized or digital assets.
• Advising a multinational financial institution on implementing artificial intelligence (AI) tools and workflows across its operations while ensuring compliance with applicable SEC, FINRA, and data governance requirements.
• Drafting comment letters on behalf of clients addressing proposed SEC and SRO rulemakings.
• Representing digital asset companies in enforcement and examination matters.
• Facilitating regulatory approvals with FINRA and the SEC for broker-dealers and digital asset companies engaging in regulated activities.

Chambers USA notes that Andrew is “well regarded for advising clients on SEC, FINRA, and other regulatory issues related to blockchain and cryptocurrency” (2026). Clients described Andrew as “the lawyer you call when you have a difficult project and you want to get the job done right the first time,” (2025) noting that “his responsiveness and updates put me at ease” (2025). Others praised that “Andrew has been my go-to for SEC-related strategy… he’s good at finding the balance between risk mitigation and business pragmatism” (2025).

Andrew’s representative matters include:

• Represented Wisdom Tree in submitting a comment letter to the SEC concerning its proposed rescission of Rule 611 and Rule 610(e) under Regulation NMS.
• Represented VanEck Digital Assets, LLC, sponsor of the VanEck BNB ETF, in connection with the registration and launch of the VanEck BNB ETF, the first U.S. spot BNB exchange-traded product.
• Represented Grove Foundation in its US$50 million anchor investment in Galaxy Digital Inc.’s inaugural tokenized CLO, Galaxy CLO 2025-1, which has financed approximately US$75 million of loans to date.
• Advised Coinbase Capital Markets Corp. on the launch of its stock trading capability for U.S. Coinbase users, including FINRA regulatory considerations and compliance measures. Announced December 17, 2026, this expansion of the Coinbase platform enables its customers to buy, sell, and manage leading stocks and ETFs alongside their crypto portfolios — with USD or USDC — all within the Coinbase app.
• Advised on broker-dealer issues related to new broker-dealer launch.
• Advised Sony Bank in relation to establishing a stablecoin business associated with Sony’s content operations.
• Represented Goldman Sachs & Co. LLC and provided regulatory advice in a collaborative initiative between the Goldman Sachs Group, Inc. and The Bank of New York Mellon Corporation to employ blockchain technology in relation to recordation of securities ownership.
• Represented Cboe Global Markets, Inc. in its acquisition of Eris Digital Holdings, LLC, an operator of a U.S.-based digital asset spot market, a regulated futures exchange, and a regulated clearing house.
• Negotiated node and technology agreements for strategic partnerships with blockchain technology companies.
• Represented issuers in global offerings of digital securities, stablecoins, digital assets, and asset-backed blockchain tokens.
• Advised Oasis Pro Markets, LLC related to U.S. regulatory requirements for its digital security alternative trading system (ATS).
• Advised INX Limited, a cryptocurrency exchange that went public on Ethereum in 2020 and issuer of the first registered security token, on broker-dealer and blockchain matters.
• Represented Brevan Howard, among others, in the launch of digital asset funds.
• Represented Paxos Trust Company, LLC in connection with its application to be the first SEC-registered clearing agency to use a blockchain technology platform to clear and settle transactions.
• Advised U.S.-cryptocurrency intermediaries and buy-side institutions with respect to digital prime brokerage offerings and lending programs.
• Advised on formation of broker-dealers and registration of alternative trading systems to transact or custody securities and digital assets.
• Negotiated trading and custody agreements for broker-dealers, banks, and other financial services companies.
• Advised client in obtaining regulatory approval to facilitate trading of security tokens or digitally enhanced securities.

• Honorary board member, Berkeley Law Foundation (formerly chief financial officer)