D. Sean McMahon

D. Sean McMahon

D. Sean McMahon Boston Tax Attorney

t. 617.906.5560

f. 617.284.6260


D. Sean McMahon is co-author of the Boston Tax Attorney Blog. Sean McMahon is a former Senior Attorney with the IRS Office of Chief Counsel and a former Special Assistant United States Attorney for Massachusetts and New Hampshire where he was responsible for tax cases. Sean has more than ten years of experience investigating and defending IRS and state tax matters and excels at resolving difficult and complex tax disputes. He counsels clients through examinations and liability disputes and, when necessary, takes disputed issues to court. Sean was named to the 2013-2016 Massachusetts Super Lawyers list in the area of tax law.

As a former IRS attorney, Sean offers clients unique insights on the real risks presented in disputes with the IRS and planning for complex transactions. He advises clients on the tax considerations of corporate, real estate, partnership, securities and option transactions. Sean also has extensive experience assisting individuals with foreign transaction reporting and penalty disputes, including foreign bank accounts and FBAR requirements.

Attorney McMahon received his LL.M. in taxation from Boston University School of Law and his J.D. cum laude from the New England School of Law where he also was a member of the Law Review.  He has also served as a council member of the Massachusetts Bar Association Tax Section.


Sean represents individuals, estates and businesses with federal and state tax issues from audit through collection.  His practice includes:

  • Examination defense, including calculation of correct tax liability, and minimizing penalties and interest
  • Collections, including installment agreements, offer in compromises, and innocent spouse
  • Appeals, including administrative appeals through the Office of Appeals and appellate courts
  • Voluntary Disclosure, including helping to bring taxpayers who have not filed returns in several years into compliance
  • Foreign Bank Accounts and FBAR Requirements, including representing U.S. citizens with dual citizenship with unreported foreign bank accounts and delinquent FBAR returns, and voluntary disclosure programs
  • Foreign Trust and Foreign Corporate interest informational returns and related non-filing penalty defense
  • Tax Litigation, including litigating tax disputes before the U.S. Tax Court, U.S. District Courts, and the U.S. Court of Federal Claims

Previous Experience

Internal Revenue Service

  • Senior Attorney IRS Office of Chief Counsel
  • Special Assistant United States Attorney for Massachusetts and New Hampshire responsible for tax cases

Professional Affiliations

  • Massachusetts Bar Association Tax Section, council member
  • American Bar Association

Speaking Engagements


  • Massachusetts Super Lawyers 2013-2017


Please visit McMahon Tax Law to contact Sean.

Leave a Reply

Your email address will not be published. Required fields are marked *