O'Driscoll was born in Clontarf on Dublin's Northside, and was educated at Blackrock College from which he was capped three times for Ireland Schools in 1996. In 1998 O'Driscoll played for the Ireland U19 side, also including his Senior teammates Donncha O'Callaghan and Paddy Wallace, which won the IRB Under-19s world championship. After leaving school, he attended University College Dublin (UCD) on a scholarship. At UCD, under director of rugby John McLean, he first made the under-20 side, before being promoted to the top team near the end of his first year. After two years, O'Driscoll graduated from UCD with a diploma in sports management. O'Driscoll made his under 21 debut in February 1999, and eventually gained four caps.

In 1999 O'Driscoll was selected for the senior squad and was on the bench for the six nations match against Italy. Although he did not play, he was selected for the summer tour to Australia during which he won his first Test cap at age 20 on 12 June 1999 in a 46-10 loss to Australia at age 20 in Brisbane. Since that day, he has established himself as one of rugby's top outside centres. It is noted that O'Driscoll played for Ireland before he played for the senior Leinster team.

O'Driscoll became so popular in Ireland that many supporters donned T-shirts bearing the motto "In BOD We Trust" (a play on "In God We Trust", the phrase that appears on all United States currency and coinage). In 2003, following the international retirement of long-time Ireland captain Keith Wood, he was awarded the captaincy. O'Driscoll then led Ireland to a second-place finish in the Six Nations, and in the process a Triple Crown.

O'Driscoll appeared in all three British and Irish Lions Tests on the team's 2001 tour of Australia. On 11 April 2005, he was named captain of the team for their 2005 tour of New Zealand. Prior to that tour he had been named captain of the Northern Hemisphere side for the IRB Rugby Aid Match (a 2004 Indian Ocean tsunami fundraiser) held at Twickenham in March 2005, but was forced to withdraw due to a shoulder injury; however, he did appear at pitchside for the match.

O'Driscoll's playing contribution to the 2005 Lions was finished in the opening minutes of the first Test against the All Blacks in Christchurch on 25 June 2005, when he was stretchered off the field with a shoulder injury just after the ball had left a ruck he was defending. Tana Umaga (captain of the All Blacks) and Keven Mealamu had combined together and lifted O'Driscoll to drive him head-first into the ground. He extended one arm to protect his head, and his shoulder was dislocated on impact.

The independent citing commissioner found that the New Zealand players had no case to answer. However, following new footage, International Rugby Board's communications manager Greg Thomas stated ...that dangerous tackles like this have no part in the game. The Lions management were heavily criticised by New Zealanders for attempting to divert attention away from their terrible performance. Although unable to play, O'Driscoll remained as non-playing captain on a losing tour and only underwent surgery on his return. He then released a DVD entitled Brian O'Driscoll's Lions Diary in which he described his tour experience and his opinion of the events that transpired.

After speculation in September 2005 that O'Driscoll was preparing to leave Irish provincial rugby and agree a contract to play in France, the IRFU quickly announced they would do all they could to keep him in Ireland. O'Driscoll subsequently signed a deal with the IRFU to keep at Leinster through the 2007 World Cup. He then signed a new contract with the IRFU that will keep him playing at Leinster until 2011. O'Driscoll made his playing comeback for Leinster in December 2005. In January 2006, he helped Leinster beat Bath to qualify for the quarter-finals of the 2005-6 Heineken Cup. On the 1st of April 2006, O'Driscoll was instrumental in leading Leinster to victory over Toulouse; reaching the Heineken Cup semi-final.

--Wikipedia