Vigorous Ethical Advocacy
that Gets Results

Ciarán O’Sullivan

Tel: (415) 391-3711

ciaran@cosullivanlaw.com

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About Ciarán O’Sullivan

Ciarán O’Sullivan has been litigating on behalf of individuals and entities in the trial and appellate courts of California since 1998.  The primary focus of the firm’s practice is resolving disputes involving the transfer of wealth on death, whether by trust, estate, intestate succession, or lifetime transfers.  We have vast experience in will contests, trust contests, disputes between fiduciaries and beneficiaries, enforcing and defending creditors’ claims, litigation involving breach of contract, breach of promises to make testamentary dispositions, ownership of real property interests, elder abuse, and complex trust and probate administration disputes.  We represent fiduciaries, beneficiaries, charitable entities, and other interest parties.   

Ciarán is currently serving a six-year term on the Executive Committee of the California Lawyers Association’s Trusts and Estates section (“TEXCOM”).  He is the Chairman of its Litigation Committee.  He was the editor of the section’s New Case Alerts from 2017 to 2021.  He was the co-chair of the Bar Association of San Francisco’s Trusts and Estates litigation committee from 2008 to 2013.  He is a frequent presenter on topics of interest to Trusts and Estates practitioners, and has authored numerous articles in the Trusts and Estates Quarterly and the Daily Journal related to trial and appellate procedure in his practice area. 

He received his undergraduate degree in Economics from University College Dublin, Ireland, and his law degree from U.C. Hastings College of the Law.

Practice Areas

Civil Litigation

Ciarán has wide experience in general commercial litigation, particularly contractual and business tort claims, real estate disputes, and litigation involving public entities.  He has successfully resolved numerous cases by means of dispositive pre-trial motions, mediations, administrative hearings, trials and appeals.

Past and Present Representative cases

  • Represent internet web-store hosting company in dispute with client on-line seller of clothing apparel.  Obtained pre-judgment writ of attachment that lead to favorable settlement for plaintiff.
  • Represent manufacturer of sheet-metal products in dispute over theft of client lists by former employees who founded a rival manufacturer.
  • Represent tax adviser in negotiating resolution of potential malpractice claim arising from the advisor’s recommendation of a tax shelter.
  • Represent San Francisco homeowners in boundary dispute with neighbor.
  • Represent seller of sightseeing tour operator in dispute arising from sale of company to rival tour operator.
  • Represent firm of International Tax Advisers/CPAs in various matters, including non-payment for professional services.
  • Represent California county government in dispute with initiative proponents regarding breach of federal civil rights law by circulating defective election materials.
  • Represent Los Angeles harbor authority in dispute with its insurers arising from environmental contamination.
  • Represent various tenants in landlord-tenant matters through Bar Association of San Francisco Volunteer Legal Services Program.

Sample Appellate Matters

  • Vargas v. City of Salinas (2009) 46 Cal. 4th 1 (wrote brief of Amicus Curiae Self-Help Counties Coalition in support of respondent City of Salinas on issue of a public entity’s right to provide information to electorate on the potential effects of a ballot initiative).

Trusts and Estates Litigation

Ciarán O’Sullivan’s practice has a particular focus on trusts and estates litigation. Ciarán handles disputes involving trustees, executors, and administrators – both private and professional.  He also represents beneficiaries, including large charitable beneficiaries, in similar matters. He has litigated suits involving oral contracts to devise property on death. In the counseling component of his practice he advises clients on dispute avoidance and alternative dispute resolution.

Ciarán also represents fiduciaries and beneficiaries in administering probate and trust estates, and in resolving disputes arising during administration.  He has significant experience in fee disputes, real property sales, forged document disputes, heirship determination petitions, will contests, trust contests, petitions for instructions and all matters governed by the California Probate Code.

Past and Present Representative Cases

  • Represent family-member successor Trustee accused of breach of fiduciary duties by omitted beneficiary.
  • Represent professional Trustee in surcharge action by heirs to California tourism landmark.
  • Represent Trustee in dispute with co-Trustee and beneficiaries over the ownership of financial accounts.
  • Represent beneficiaries of Trust in surcharge action against professional Trustee for excessive trustee fees and other breaches of duty.
  • Represent omitted child in case of first impression in California as to application of omitted child statute to situation where father denies paternity of child notwithstanding a valid paternity order.
  • Represent omitted relatives of decedent in will contest and breach of contract action alleging breach of promise by decedent to leave estate to caregiver relatives where decedent instead left estate to charity – obtained $1.7 settlement for relatives.
  • Represent charitable foundation in defending undue influence claim by omitted family member.

Sample Appellate Matters

  • Murphy v. Murphy (2008) 164 Cal.App.4th 376 (wrote successful Petition for Writ of Supersedeas on behalf of Appellant).
  • Estate of Bartsch (2011) 193 Cal.App.4th 885 (represented Appellant)
  • Grappo v. McKean&McMills LP 2012 Cal. App. Unpub. Lexis 6825 (represented Appellant)
Education & Admission

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Publications and Presentations

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Professional Involvement, News

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The Law Office of Ciarán O’Sullivan

50 California Street, 34th Floor
San Francisco, CA 94111

Tel: (415) 391-3711
Cell: (415) 602-4635
Fax: (415) 513-0449
ciaran@cosullivanlaw.com