Sean McMahon

Top rated Tax attorney in Boston, Massachusetts

McMahon & Tivnan, PC
Sean McMahon
McMahon & Tivnan, PC

Practice Areas: Tax; view more

Licensed in Massachusetts since: 1994

Education: New England Law | Boston

Selected to Super Lawyers: 2013 - 2024
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McMahon & Tivnan, PC

100 High St
Ste 2601
Boston, MA 02110 Visit website


D. Sean McMahon is the founder of McMahon & Tivnan, PC, located in Boston, Massachusetts. Focusing his practice exclusively on federal and state tax matters, he provides representation to both businesses and individuals at every stage of the audit process. Mr. McMahon also advises clients on the tax consequences of complex business, real estate and financing transactions.

Mr. McMahon graduated from Fairfield University with his Bachelor of Arts in psychology and economics. He then pursued his legal studies at New England Law | Boston and was awarded his Juris Doctor cum laude in 1994. While in law school, he served on the New England Law Review. Admitted to practice in Massachusetts and before the U.S. Tax Court, Mr. McMahon also holds an LL.M. in taxation from Boston University School of Law.

Before entering private practice, Mr. McMahon garnered experience first working as a special assistant U.S. attorney prosecuting tax cases in Massachusetts and New Hampshire before working as a senior attorney with the IRS Office of Chief Counsel. He has defended his clients in their complex tax disputes, and is often able to negotiate significantly reduced penalties and offers in compromise. His work also includes helping people who have not filed returns for several years come into compliance through voluntary disclosure. Other matters include helping clients with their FBAR matters, including those who have unreported foreign bank accounts.

Mr. McMahon is an active participant in several professional organizations, and he has been a member of the Taxation Law Section of the Massachusetts Bar Association since 2007. 

Practice areas

Tax: Business, Tax: Consumer

Focus areas

Tax Law

  • 50% Tax: Business
  • 50% Tax: Consumer

First Admitted: 1994, Massachusetts

Professional Webpage:

Educational Background:
  • Fairfield University, B.A. in Psychology and Economics
  • Boston University School of Law, LL.M. in Taxation
Scholarly Lectures/Writings:
  • Panelist, "The Madoff Mess" Massachusetts Continuing Legal Education, Inc. (MCLE), 2009
  • Speaker, “Correcting United States Income Tax and Foreign Asset Reporting Problems,” Massachusetts Society of Enrolled Agents, 2017
  • Speaker, “Correcting IRS Income Tax and Foreign Asset Reporting Problems”, 2016
  • Panelist, “Ethical Considerations in Individual and Family Representation,” ABA Section of Taxation and Section of Real Property, Trust & Estate Law, Trust & Estate Division 2016 Joint Fall CLE Meeting, 2016
  • Faculty Member/Speaker, Navigating the Madoff Recovery Maze, 2009
  • Panelist, "What Every CPA Needs to Know About Civil and Criminal Tax Litigation," CPE Credit Program for Certified Public Accountants, 2010 and 2011
  • Panelist, Working with Overseas Americans and Foreign Nationals in the United States and IRS Voluntary Disclosure Program Update," CPE Credit Program for Certified Public Accountants, 2012
  • Panelist, "The IRS Voluntary Off-shore Disclosure Initiative," CPE Credit Program for Certified Public Accountants, 2010
  • Speaker, “Avoiding Tax Problems for a New Business,” Eighth Business Fundamentals Bootcamp, 2013
  • Speaker, "Correcting IRS Income Tax and Foreign Asset Reporting Problems," Kuwait, 2014
  • Named to the Massachusetts Super Lawyers List
Bar/Professional Activity:
  • U.S. District Court for the District of Massachusetts
  • American Bar Association
  • Council Member, Massachusetts Bar Association Tax Section, 2007
  • U.S. Bankruptcy Court
  • Massachusetts
  • U.S. Tax Court
Pro bono/Community Service:
  • Counsel, Motivating Miles Foundation
Verdicts/Settlements (Case Results):
  • Megibow v. Commissioner, T.C. Memo 2004-41
  • Enos v. Commissioner, 123 T.C. 17
  • Irvin v. Commissioner, T.C. Summary Op. 2004-108
  • Sinele v. Commissioner, T.C. Memo 2004-137
  • Feinberg v. Commissioner, T.C. Memo 2003-304
  • Bourbeau v. Commissioner, T.C. Memo 203-117
  • Lewin v. Commissioner, T.C. Memo 2003-305
  • Cohen v. Commissioner, T.C. Memo 2003-303
  • The United States Court of Appeals for the First Circuit ruled in favor of McMahon & Associates’ client, Robyn Baker, in a tax dispute involving the division of assets in a divorce. The case is United States v. Scott G. Baker, Robyn Baker. The defendant, Scott G. Baker divorced his wife, Robyn Baker, in 2008 in order to fraudulently transfer assets and avoid some of his tax liability. The defendant owed more than $5 million dollars to the Internal Revenue Service (IRS) as a result of an agreed judgment in 2015. The government argued that its tax liens attached to the defendant’s assets and to some of Ms. Baker’s assets too. Ms. Baker’s attorney, D. Sean McMahon said, “I am pleased the First Circuit Court of Appeals agreed with us that Ms. Baker is entitled to her equitable share of marital assets. By affirming our trial victory over the IRS on it’s positions of sham divorce and tax lien tracing, the First Circuit has finally put to rest the government’s attempt to seize our client’s assets to pay her ex-husband’s tax debt.“ The district court set aside the Baker’s separation agreement as a fraudulent transfer and re-divided and reallocated the couple’s assets under Massachusetts law. The First Circuit reviewed the district court’s 50/50 allocation of the Baker’s escrowed funds and their home in Hingham, MA and found that: 1.  The government was not entitled to Ms. Baker’s half of the proceeds from the sale of the Hingham property and affirmed the district court’s ruling that the government had not submitted evidence sufficient to support a lien-tracing theory. 2.  It is not clear that the district court considered the fourteen factors required by Massachusetts law to arrive at an equitable division of the parties’ assets. Therefore, the division of the escrowed funds is vacated and remanded back to the district court to hear the case again. Additionally, the First Circuit’s decision noted: “As will become clear in this opinion, Robyn appears to be implicated in at least some of Scott’s fraudulent activity. However, she was never put on trial, and it appears that the government is not pursuing any claims for fraud against her. As such, nothing in this opinion is meant to suggest that Robyn has been found guilty of fraud.”Read the full decision., 2016

Office location for Sean McMahon

100 High St
Ste 2601
Boston, MA 02110

Phone: 617-600-5400


12 Years Super Lawyers
  • Super Lawyers: 2013 - 2024

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