There have been four Baronetcies created for persons with the surname O'Brien, one in the Baronetage of Ireland and three in the Baronetage of the United Kingdom.

The O'Brien Baronetcy, of Leaghmenagh in the County of Clare, was created in the Baronetage of Ireland on 9 November 1686. For more information on this creation, see the Baron Inchiquin

Baron Inchiquin

Baron Inchiquin is one of the older titles in the Peerage of Ireland. It was created in 1543 for Murrough O'Brien, Prince of Thomond, who was descended from the great high king Brian Boru)...

.

The O'Brien Baronetcy, of Merrion Square in Dublin and Boris-in-Ossory in Queen's County, was created in the Baronetage of the United Kingdom on 25 September 1849 for Timothy O'Brien. He was a merchant, Lord Mayor of Dublin

Lord Mayor of Dublin

The Lord Mayor of Dublin is the honorific title of the Chairman of Dublin City Council which is the local government body for the city of Dublin, the capital of Ireland. The incumbent is Labour Party Councillor Andrew Montague. The office holder is elected annually by the members of the...

 and Liberal

Liberal Party (UK)

The Liberal Party was one of the two major political parties of the United Kingdom during the 19th and early 20th centuries. It was a third party of negligible importance throughout the latter half of the 20th Century, before merging with the Social Democratic Party in 1988 to form the present day...

 Member of Parliament

Member of Parliament

A Member of Parliament is a representative of the voters to a :parliament. In many countries with bicameral parliaments, the term applies specifically to members of the lower house, as upper houses often have a different title, such as senate, and thus also have different titles for its members,...

 for Cashel

Cashel (UK Parliament constituency)

Cashel is a former British Parliament constituency in Ireland, returning one MP. It was an original constituency represented in Parliament when the Union of Great Britain and Ireland took effect on 1 January 1801....

. The second Baronet represented King's County

King's County (UK Parliament constituency)

King's County was a parliamentary constituency in Ireland, represented in the House of Commons of the United Kingdom. It return two Members of Parliament 1801–1885 and one in 1918–1922.-Boundaries:...

 in the House of Commons

British House of Commons

The House of Commons is the lower house of the Parliament of the United Kingdom, which also comprises the Sovereign and the House of Lords . Both Commons and Lords meet in the Palace of Westminster. The Commons is a democratically elected body, consisting of 650 members , who are known as Members...

 as a Liberal for over thirty years. The third Baronet was a Deputy Lieutenant

Deputy Lieutenant

In the United Kingdom, a Deputy Lieutenant is one of several deputies to the Lord Lieutenant of a lieutenancy area; an English ceremonial county, Welsh preserved county, Scottish lieutenancy area, or Northern Irish county borough or county....

 of County Cork

County Cork

County Cork is a county in Ireland. It is located in the South-West Region and is also part of the province of Munster. It is named after the city of Cork . Cork County Council is the local authority for the county...

. As of 2007 the presumed seventh and present Baronet has not successfully proven his succession and is therefore not on the Official Roll of the Baronetage, with the baronetcy considered dormant. For more information, follow this link.

The O'Brien Baronetcy was created in the Baronetage of the United Kingdom on 28 September 1891. For more information on this creation, see the Baron O'Brien.

The O'Brien Baronetcy was created in the Baronetage of the United Kingdom on 15 January 1916. For more information on this creation, see the Baron Shandon.

O'Brien Baronets, of Merrion Square and Boris-in-Ossory (1849)

• Sir Timothy O'Brien, 1st Baronet (1787–1862)
• Sir Patrick O'Brien, 2nd Baronet
  Sir Patrick O'Brien, 2nd Baronet
  Sir Patrick O'Brien, 2nd Baronet was an Irish politician.He was elected in 1852 as a Member of Parliament for King's County , and held the seat until the constituency was divided at the 1885 general election....
  
   (1823–1895)
• Sir Timothy Carew O'Brien, 3rd Baronet
  Sir Tim O'Brien, 3rd Baronet
  Sir Timothy "Tim" Carew O'Brien, 3rd Baronet was born at Dublin on 5 November 1861 and died at Ramsey, Isle of Man on 9 December 1948. He was an Irish baronet who played cricket for England in five Test matches....
  
  (1861–1948)
• Sir Robert Rollo Gillespie O'Brien, 4th Baronet (1901–1952)
• Sir John Edmond Noel O'Brien, 5th Baronet (1899–1969)
• Sir David Edmond O'Brien, 6th Baronet (1902–1982)
• Sir Timothy John O'Brien, 7th Baronet (b. 1958)