Person Photo
Person Photo

William Colgin


555 17th Street, Suite 3200, Denver, CO 80202
645 South Cache Street, Suite 100, P.O. Box 68, Jackson, WY 83001

Bill represents corporate taxpayers in complex, high-stakes federal tax controversies and tax litigation with significant implications for his clients’ bottom line.

Bill litigates in the US Tax Court, federal district courts, state courts, and appellate courts throughout the country. His cases and controversies typically involve high dollar amounts and tend to include international tax, transfer pricing, intellectual property, economic substance, and other high-profile areas of tax dispute.

Bill began his tax litigation career as a trial attorney in the Tax Division of the US Department of Justice and he draws on that experience to represent clients in complex Internal Revenue Service (IRS) examinations and appeals, anonymous IRS disclosure disputes negotiations, and coordinated resolution of multistate state tax issues. Bill continues to defend clients in federal criminal and civil tax investigations by the Tax Division of the US Department of Justice or the US Attorney’s Offices around the country.

Prior to joining Holland & Hart, Bill was a partner at Morgan Lewis.


Tax Litigation and Controversy
  • High profile tax litigations involving deficiency and refund suits
  • Examination defense involving complicated and contentious issues
  • Extensive IRS Appeals negotiations
  • Anonymous IRS disclosure disputes
  • Qui Tam suits involving tax-related claims
  • False Claim Acts suits, both single-state and multistate
  • Coordinated management and resolution of multistate tax issues, including amnesty programs



Speaking Engagements


Bar Admissions

Court Admissions


  • The Best Lawyers in America©, Tax Law, 2023
  • Chambers USA, Tax, Colorado, 2020-2022
  • Chambers USA, Litigation: General Commercial, Wyoming, 2019-2022
  • Chambers USA, Litigation: General Commercial, Colorado, 2019-2020
  • Chambers USA, Tax, California, 2008-2018
  • Chambers USA, Tax: Controversy, Nationwide, 2008-2018
  • The Legal 500 US, Tax – US Taxes – Contentious, 2011–2015, 2017

Professional and Civic Affiliations

  • California Bar, Executive Committee, Taxation Section, Past Vice Chair
  • Tax Court Pro Se/Pro Bono Program, San Francisco, California, Past Director
  • American Bar Association, Tax Section, Technology Subcommittee, Past Chair
  • American Bar Association, Tax Section, Court Practice and Procedure Committee, Past Member
  • Advisory Board for the University of San Diego School of Law Procopio International Tax Institute, Past Member
Widget Image

Unless you are a current client of Holland & Hart LLP, please do not send any confidential information by email. If you are not a current client and send an email to an individual at Holland & Hart LLP, you acknowledge that we have no obligation to maintain the confidentiality of any information you submit to us, unless we have already agreed to represent you or we later agree to do so. Thus, we may represent a party adverse to you, even if the information you submit to us could be used against you in a matter, and even if you submitted it in a good faith effort to retain us.