O'Beirne received his country's highest award for bravery during combat, the Medal of Honor, for actions taken on June 1, 1862 during the Battle of Fair Oaks.

He was born in Cappagh, County Roscommon, Ireland, to Michael Horan O'Beirne and Eliza Rowan O'Beirnehe was nine months-old he when his family emigrated to New York City.

[3] He continued on to study philosophy and then law at St. John's and received his Magister Artium (MA) and Legum Doctor (LL.D) in 1857.

[4] When the Civil War broke out in April 1861, the self-described radical Republican originally enlisted as a private in Company I of the 7th New York Militia but was mustered out two months later.

They camped at the foot of East Capitol Street.,[5] Their regimental commander, John H McCune,[note 1] as the senior colonel was initially the brigade commander, but he was relieved for cause, court-martialed, and found guilty of conduct "prejudicial to the good order and military discipline" though also directed to "resume his sword and duties.

After the defeat at Bull Run, 1861, Lincoln relieved McDowell and appointed George B. McClellan as his new commander of the army at the capital.

During the summer and fall, McClellan brought a high degree of organization to his new army, and greatly improved its morale with frequent trips to review and encourage his units.

[note 5] After several temporary assignments the regiment finally became a part of the 3d brigade, 3rd division, III Corps from March 13, 1862.

During the Seven Days at Oak Grove, leading Company C, O'Beirne performed the actions that would earn him the Medal of Honor.

[note 9] After spending six weeks in camp with the rest of the AoP, O'Beirne and the 37th found themselves leaving the Peninsula suffering a strategic feat.

[15] O'Beirne and his regiment were present but in reserve at Second Bull Run and Chantilly during MGEN Pope's Northern Virginia campaign.

They joined the rest of the AoP, now commanded by Burnside reached Falmouth, across the Rappahannock from Fredericksburg on Saturday, December 6, 1862.

Despite sound strategy, the offensive failed due to dissension among generals in the Army of the Potomac, compounded by severe winter storms.

As O'Beirne and his compatriots slogged through the mud, Lee ample time to line the other shore with his army, although there was no attempt to interfere with his crossing except from the sharpshooters, who peppered away on all occasions.

Burnside finally became resigned the failure and gave the order for the army to return to its camp in Falmouth on Monday, January 26.

On May 3 while the brigade was moving to the rear of the Union lines, a deadly attack on the front and left flank caused confusion and forced the regiment to fall back.

In April 1865 he was serving as Provost Marshall of Washington DC and was active in the pursuit and capture of John Wilkes Booth and his associate conspirators following the assassination of US President Abraham Lincoln.

In September 1865 he was brevetted to the rank of brigadier general for "gallant, distinguished and meritorious service" while serving in the Union Army during the Civil War and he was discharged from military duty on January 30, 1866.

He died in New York City at the age of 77 The President of the United States of America, in the name of Congress, takes pleasure in presenting the Medal of Honor to Captain James Rowan O'Beirne, United States Army, for extraordinary heroism on May 31 & 1 June 1862, while serving with Company C, 37th New York Infantry, in action at Fair Oaks, Virginia.

[3] In March 1889, fellow veteran and GAR member, President Benjamin Harrison appointed him Assistant Commissioner of Immigration at Ellis Island.

He was active in veterans' affairs; he served a term as the Grand Marshal of the GAR Posts of New York state.

He contributed articles to the alumni magazine and was a common sight on the Bronx campus until shortly before his death in Manhattan at the age of 77, on February 17, 1917.