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About me

Mr. O’Leary has extensive experience in a wide variety of products liability, subrogation, employment, personal injury, general commercial litigation, insurance bad faith, and workers’ compensation claims.


Languages spoken: English, French

Practice areas


  1. Litigation: 100%
    29 years, 2 thousand cases



Hourly ($175-500/hour)

Payment types:

Cash, Check

Attorney endorsements

2 total 

Are you an attorney? Endorse this lawyer

  • Scott Gregory Hoy

    I have worked with Mark on the other side of cases, and have seen his work as a Plaintiff lawyer. He knows the law well, and does an admirable job.


    Scott Hoy Personal Injury Attorney
    Relationship: Worked together on matter

  • John M O'Brien

    I endorse this lawyer. An extremely talented and well respected attorney in the legal community.


    John O'Brien Personal Injury Attorney
    Relationship: Fellow lawyer in community

Contact info

O'Leary Law Office

3500 S Phillips Ave Ste 120
Sioux Falls, SD, 57105-6864


SDAuthorized to practice law199411/12/2013
TXEligible To Practice In Texas 198810/19/2015
MNAuthorized to practice198607/31/2015
We have not found any instances of professional misconduct for this lawyer.
Avvo contributions
Legal answers
Work experience
TitleCompany nameDuration
OwnerO'Leary Law Office1991 - Present
AssociateJardine Logan & O'brien, PLLP1990 - 1992
AssociateHirsch Glover Robinson & Sheiness1988 - 1991
Association namePosition nameDuration
South Dakota Defense Lawyers AssociationPresident2014 - 2015
Defense Research InstituteMember2005 - Present
South Dakota State BarMember1993 - Present
State Bar of TexasMember1988 - Present
Minnesota State Bar AssociationMember1986 - Present
School nameMajorDegreeGraduated
William Mitchell College of LawLawJD - Juris Doctor1986