Frederick Ryan Castillo is a partner in Mayer Brown’s New York office and a member of the Capital Markets practice. His work focuses on securities and corporate finance transactions. Ryan advises issuers, investment banks and sponsors in connection with public offerings and private placements of debt, equity and hybrid securities, including initial public offerings, follow-on offerings, investment grade and high-yield debt offerings, private investment in public equity, tender and exchange offers, consent solicitations, medium term note programs and other capital markets transactions in the United States, Canada and the Euro markets. He represents companies and financial intermediaries involved in a broad range of industries, including financial services, technology, telecommunications, retail, life sciences, real estate and energy.

Ryan earned his Master of Laws degree with a concentration in international finance from Harvard Law School, where he served as an editor of the Harvard Business Law Review. He earned his JD with honors from the Ateneo de Manila Law School, where he served as captain of the World Champion team in the 45th Philip C. Jessup International Law Moot Court Competition. He holds a BA in Economics, with honors, from the Ateneo de Manila University. Ryan was previously an associate in the capital markets group of another global law firm in New York. Prior to that, he was a corporate associate in a regional law firm headquartered in Singapore, where he worked on capital markets and cross-border transactions for clients across the Asia-Pacific.

Ryan is co-author of A Deep Dive Into Capital Raising Alternatives (2020) and author of Non-GAAP Explained (2017), published by the International Financial Law Review. He regularly writes on securities law issues and has authored a number of capital markets-related pieces, including Debt Capital Markets in the United States: Regulatory Overview (2019) published by Practical Law, Top 10 Practice Tips: Comfort Letters (2018) published by Lexis Practice Advisor and The Coconundrum (2011) published by the Harvard Business Law Review.

Ryan is named a “Rising Star” for the Americas in the Capital Markets category in Euromoney’s Expert Guides: Rising Stars for 2021 and 2022. He was also named a “Rising Star” in the capital markets category by Euromoney in its Rising Stars Americas Awards 2020. Ryan is ranked as a “Rising Star Partner” by IFLR1000 2022 for Capital Markets: Debt and Capital Markets: Equity in the United States, and had previously been ranked as a “Rising Star” for the same by IFLR1000 2021, 2020,  and 2019. The Legal 500 US also named him a “Next Generation Partner” (2021), “Rising Star” (2020), and he is a  recommended lawyer for Capital Markets: Debt. Ryan is recognized by Best Lawyers: Ones to Watch 2021 for his work in Securities and Capital Markets law in the United States.


Ateneo de Manila University, BA, with honors

Ateneo de Manila University, JD, with honors
Captain of the World Champion team in the 45th Philip C. Jessup International Law Moot Court Competition

Harvard Law School, LLM
Editor, Harvard Business Law Review


  • New York
  • Philippines