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Mark D. O'Leary

Litigation Attorney at Sioux Falls, SD

5.0   7 reviews

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About Mark

Learn Mark’s areas of practice.

Practice areas
  1. Car accident

    37 years

  2. Lawsuits and disputes

  3. Litigation
    General Practice of law with emphasis on civil litigation, insurance claims, commercial litigation, and problem solving through the application of sound practices of alternative dispute resolution. Licensed in South Dakota, Minnesota, Texas, and the Federal Courts.

    37 years

  4. Personal injury

    37 years

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

Licensed for 36 years
State SD
Status Active
Acquired 1994
Updated 11/12/2013
State TX
Status Eligible to Practice in Texas
Acquired 1988
Updated 01/25/2023
State MN
Status Authorized to Practice
Acquired 1986
Updated 01/24/2023

We have not found any instances of professional misconduct for this lawyer.

Contact Mark

O'Leary Law Office
3500 S Phillips Ave Ste 120
Sioux Falls, SD, 57105-6864


5.0 / 5.0
  7 customer reviews
5 Star
4 Star
3 Star
2 Star
1 Star
Posted by Yvonne | May 2, 2021
This review is from a person who hired this attorney.
| Hired Attorney
Mark O’Leary is exceptional! Great advisor and consummate professional. Highly knowledgeable and experienced in litigation matters. Dependable and fair. Mr O’Leary is personable and easily relatable individual. Felt very comfortable working with him. Highly recommend for any business or individual legal matters.
Posted by Lidia | October 8, 2020
This review is from a person who hired this attorney.
| Hired Attorney
Proficient attorney
Mark O'Leary managed to successfully navigate around the obstacles and brought the case to the positive resolution.
Posted by Aaron | October 7, 2020
This review is from a person who hired this attorney.
| Hired Attorney
Litigation work
Mark is an amazing attorney that helped me out of the worst time in my life. I would highly recommend him. He is an extremely bright and level-headed litigator who wants to do what is in your best interest.
Posted by anonymous | January 18, 2014
Business Opportunity
My husband and I hired Mark O'Leary to help us make an informed decision regarding a new business investment. Mark was able to patiently explain the pros and cons of each aspect of the new venture. Mark also helped to make sure that we were legally protected from any fall out with the first owners, and created a very specific contract for us. Our situation required quite a bit of research on his part, since it involved a foreign owned business in North Africa, not exactly a typical client request for him. With Mark's advice and his thoroughness of reviewing all factors in this situation we felt confident to move forward. I would highly recommend Mark for any legal advice that you might need.
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Posted by Bill | January 16, 2014
Great Attorney
Mark O'Leary has represented me for several years. First class gentleman and very smart Attorney. Mark's input will help you make solid legal decisions. He will always be thinking in your best interest. I would recomend Mark to anyone. You won't be disappointed.
Posted by Chris | November 27, 2013
Top Litigator
Mr. O'Leary is truly an excellent attorney on all counts. He is a gentleman and well respected by his peers. He is known for his straight forward approach in communications and his superior knowledge of the law. Mark does not hip shoot his opinions and prepares well for trials. He is very fair and honest in billings practices and places his client's interests above his own. In my profession, I have occasion to work with attorneys in multiple jurisdictions and have found Mark to be one of the finest and a pleasure to work with in all instances over the past 20 plus years. I have utilized his services for my businesses, my personal matters as well as recommended him frequently to my clients and business associates.
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Posted by Robin | November 21, 2013
Client focused and 100% professional.
Mark O'Leary has represented me and my business since 1999 and has done so in an exemplary manner. He is very easy to talk to, quick to understand the issues and give excellent guidance even sometimes towards another attorney if he feels it serves the needs of the client better. Mark is very focused on what is best for his client which is why I go back to him whenever I have need of legal advice and services. I trust him completely and would not hesitate to recommend his legal services to friends and family.
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  • Hourly Rates $ 175-500 per hour
Payment methods
Cash, Check


AVVO RATING 10.0 (Superb)

Work Experience

  • Owner
  • O'Leary Law Office
  • 1991 - Present
  • Associate
  • Jardine Logan & O'brien, PLLP
  • 1990 - 1992
  • Associate
  • Hirsch Glover Robinson & Sheiness
  • 1988 - 1991


  • William Mitchell College of Law
  • JD - Juris Doctor
  • 1986


  • South Dakota Defense Lawyers Association
  • Board of Directors
  • 2010 - Present
  • Defense Research Institute
  • Member
  • 2005 - Present
  • South Dakota State Bar
  • Member
  • 1993 - Present
  • State Bar of Texas
  • Member
  • 1988 - Present
  • Minnesota State Bar Association
  • Member
  • 1986 - Present
  • South Dakota Defense Lawyers Association
  • President
  • 2014 - 2015
View all associations

Languages Spoken

  • English

Honors and Awards

  • Distinguished
  • Martindale-Hubbell
  • 2016
  • Exceptional Performance Citation
  • Defense Research Institute
  • 2015
  • Exceptional Performance Citation
  • Defense Research Institute
  • 2014

Attorney endorsements

Received (3)
Given (2)
Endorse Mark
Lawsuits and disputes Attorney | Jan 05
Relationship: Worked together on matter
"I endorse Mark. We have worked on the opposite side of cases, so I know he always brings his "A" game. Mark is a highly skilled attorney who is equally professional and ethical in all the work he does."
Personal injury Attorney | Nov 03
Relationship: Worked together on matter
"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."
Litigation Attorney | Aug 08
Relationship: Fellow lawyer in community
"I endorse this lawyer. An extremely talented and well respected attorney in the legal community."
Personal injury
Personal injury