O'Brien, the reigning ERC European Player of the Year, follows in the footsteps of a number of his current Ireland team-mates in being honoured by the Irish rugby writers.
Previous winners of the award have included Gordon D'Arcy (2004), Ronan O'Gara (2005 and 2008), Paul O'Connell (2006), Felipe Contepomi (2007), Brian O'Driscoll (2009) and Tommy Bowe (2010).
Also on the night, Ireland's most-capped Women's international Lynne Cantwell was named Women's Player of the Year after another outstanding season at centre.
Ulster Bank League champions Old Belvedere were honoured as the Club of the year and Leinster picked up the Dave Guiney perpetual award as Team of the Year in recognition of their Heineken Cup Success.
The Tom Rooney award for making an exceptional contribution to the game had a very deserving recipient in Alan Lewis. His refereeing record includes two World Cups and a record number of European Cup matches.
The two new members inducted to the Guinness Rugby Writers of Ireland Hall of Fame were former Ireland out-half Ollie Campbell and winger Mick Lane.
Peter O'Brien of Guinness and Brendan Fanning, Chairman of the Rugby Writers of Ireland, jointly presented the awards.
2011 GUINNESS RUGBY WRITERS OF IRELAND AWARD WINNERS:
PLAYER OF THE YEAR -
In the 2010/11 season, Sean O'Brien started all of Leinster's nine Heineken Cup matches, scoring four tries and picking up three man-of-the-match awards along the way to overall success in Cardiff in May.
O'Brien also started all of the 2011 Six Nations matches, this time picking up the man-of-the-match award against Italy.
He earned his first cap for Ireland against Fiji in the RDS in 2009 with a second cap coming soon after against South Africa.
CLUB OF THE YEAR -
Old Belvedere was founded in 1930, and has made a huge contribution to Irish rugby since then. Several world class internationals and a large number of administrators and referees have been spawned by the Anglesea Road club.
Before this year their proudest boast was winning seven Leinster Cups in-a-row in the 1940s, but this year's achievement was up there with that amazing and unequalled run of victories.
Having been demoted to the second tier, they not only won their way back but went through this year's Ulster Bank League to win the whole thing with an impressive victory over Cork Constitution in the Division 1 final.
DAVE GUINEY AWARD (TEAM OF THE YEAR) -
Leinster completed an extraordinary comeback when they stormed back from a 16-point half-time deficit against Northampton to win 33-22 and lift the Heineken Cup for the second time in three years.
Leinster reached the Magners League grand final at Thomond Park against table toppers Munster, after finishing second in the league format and beating Ulster in their semi-final clash. However, Joe Schmidt's men were beaten by Munster 19-9.
TOM ROONEY AWARD (FOR SERVICES TO RUGBY) -
Alan Lewis has announced his intention to retire from refereeing at the end of this season. With 45 major international Test matches to his credit, including a Rugby World Cup quarter-final and games across the RBS 6 Nations Championship and Tri Nations, Lewis is one of the longest serving IRFU international referees.
He also holds the record for matches in European competition with an incredible 83 matches, 71 of which were Heineken Cup games including three semi-finals and the Heineken Cup final in 2007.
GUINNESS HALL OF FAME -
Mick Lane was a member of the great Ireland team of the late 1940s and early 1950s, missing out on the 1948 Grand Slam through injury but he was part of the side that took the Triple Crown in 1949, and the side that narrowly missed another Grand Slam in 1951.
In all he won 17 caps between 1946 and 1953 and was picked for the Lions tour in 1950, and was capped against both New Zealand and Australia.
Ollie Campbell was first capped in 1976 and had to wait until 1979 to be capped again, this time controversially Down under against Australia where he was preferred to the incumbent, Tony Ward. Campbell more than justified his selection by kicking Ireland to a series win.
Ollie then became a fixture on the Irish side although the selectors tried to accommodate both himself and Tony Ward, but it was Campbell who wore the number 10 jersey as he played a major part in the acquisition of Ireland's first Triple Crown since 1949 in the 1982 season.
He had a hand in most of the significant and memorable moments of that campaign, including scoring all of Ireland's points against Scotland. A staunch member of Old Belvedere, he was captain of the club from 1979 to 1981.
He won 22 caps for Ireland and another six for the Lions, and was a huge contributor to the fabric of the Irish rugby even after he had retired from playing.
WOMEN'S PLAYER OF THE YEAR -
Lynne Cantwell only took up rugby late in life when she went to University of Limerick to study sports science. Since taking up the game, her influence on the Irish Women's rugby scene has been remarkable.
So far, she has been the most influential personality Ireland has had since the start of Women's rugby transforming the national side into a highly competitive unit and becoming Ireland's most-capped player.
She lives in London now, where she is active with the Wooden Spoon Charity Sevens team, who travel all over the UK and have beaten the Women's national side three times this year.