ANDREW SIOSON advises clients on a broad range of regulatory, compliance, enforcement, and transactional matters. In this capacity, he has represented 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 various other state and federal regulators. Andrew’s practice also focuses on issues related to cryptocurrency, tokenized assets, and blockchain/distributed ledger technology.
Prior to joining Sidley, Andrew served as special counsel at the SEC in the Division of Trading and Markets. He gained particular experience in supervision of equities and options exchanges, alternative trading systems, broker-dealers, and other major securities market participants. Among many issues, Andrew worked on an SEC rulemaking related to order handling disclosures, market structure reform, FINRA and other self-regulatory organization (SRO) rule changes, market data and National Market System (NMS) plan governance, exchange-traded fund (ETF) listing standards, and issues related to Dodd-Frank Act implementation. During his time at the SEC, Andrew received a Director’s Award for work related to security-based swaps. Before joining the SEC, he gained experience as a corporate lawyer at a firm in New York, practicing primarily in private funds, finance, and mergers and acquisitions.
Andrew is a registered certified public accountant (CPA) and has held a Series 7 license.
Andrew’s financial services and digital asset practice includes:
- Advising broker-dealers on a variety of regulatory matters and examination or enforcement issues, including with respect to 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 alternative trading systems (ATSs), clearing agencies, transfer agents, and national securities exchanges, including those seeking to facilitate the trading of traditional securities and tokens or other digital assets.
- Drafting comment letters on behalf of clients on a broad range of proposed SEC and self-regulatory organization rules.
- Representing digital asset companies with respect to enforcement and examination issues.
- Facilitating regulatory approvals with FINRA and the SEC on behalf of existing broker-dealers and digital asset companies intending to participate in regulated activities.
Andrew is a member of the firm’s top-ranked Securities Enforcement and Regulatory practice which has been ranked Band 1 for Nationwide Financial Services Regulation: Broker-Dealer (Compliance & Enforcement) by Chambers USA since 2013. The practice has also been repeatedly named “Compliance Practice Group of the Year” by Law360, as well as “Law Firm of the Year” for both Securities Regulation and Litigation — Regulatory Enforcement by U.S. News — Best Lawyers®, most recently in 2024 and 2025. Andrew is individually ranked by Chambers FinTech for USA Nationwide FinTech Legal: Blockchain & Cryptocurrencies (2025). Clients in the 2025 edition noted that “Andrew is the lawyer you call when you have a difficult project and you want to get the job done right the first time. His responsiveness and updates put me at ease.” Clients also told Chambers USA that “Andrew has been my go-to for SEC-related strategy and his guidance was really helpful for us as he worked at the SEC. He’s good at finding the balance between risk mitigation and business pragmatism” (2025). Best Lawyers: Ones to Watch® in America has recognized Andrew for his work in Securities Regulation (2026).