O'Brien was presented with his award, a specially struck gold medal, by ERC chief executive Derek McGrath at a ceremony at the player's home ground, the RDS.
"Sean was an inspirational character at the heart of the Leinster pack in their victorious Heineken Cup season and proved himself to be a major force both as a ball carrier and defender," said McGrath.
"He played across the back row, scored vital tries and picked up three Heineken Man of the Match awards. His power, athleticism and consistency over the course of the Heineken Cup made him an excellent choice for the ERC European Player of the Year Award."
In 2010 ERC, the governing body of Europe's two club rugby tournaments, launched the highly acclaimed ERC15 Awards, recognising the efforts of a number of outstanding contributors to the first decade and a half of European competition. The inaugural recipient of theERC European Player Award, as the best player over the first 15 years of these tournaments, was Munster's Ronan O'Gara.
For the 2010/11 season ERC opted to present one award to recognise the best player of the season from both of its tournaments - the Heineken Cup and Amlin Challenge Cup - selected by a panel of five experts.
The Selection Panel comprised three members of last year's ERC15 Awards committee, Stuart Barnes (Sky Sports), Jean-Roger Delsaud (Midi Olympique) and Stephen Jones (Sunday Times). They were joined by Heineken Cup Ambassador, Raphael Ibanez, and Gerry Thornley (Irish Times).
After studying the performances of players from the 24 Heineken Cup and 20 Amlin Challenge Cup teams in this season's campaign the Selection Panel presented a five man shortlist to ERC:
• Jamie Heaslip Leinster
• Isa Nacewa Leinster
• Sean O'Brien Leinster
• Sergio Parisse Stade Francais Paris
• Soane Tonga'uiha Northampton Saints
The shortlist was also presented to the 44 clubs and their recommendations were factored into the deliberations of the Selection Panel which reconvened in Cardiff, host city for the two European finals, to complete the selection process. The winner was confirmed after all five shortlisted candidates had been seen in action in the two finals.
"It's been a fantastic year for me, and more importantly for Leinster," said O'Brien. "It's great to be presented with an award like this, but it has more to do with the team than it has to do with me. Hopefully, this is only the start rather than the end of our success in Europe, and of course, we've got another trophy to aim at this weekend."
SEAN O'BRIEN FACTFILE
Born: 14 February, 1987, Ardistan, County Carlow
Height: 1.88 m (6' 2")
Weight: 108 kg (16 st 13 lb)
School: Tullow Community School
Clubs: UCD, Tullow
Ireland Caps: 9 (W7,L2)
Test Debut: Ireland v Fiji at Dublin, 21 November, 2009
Sean won caps for Ireland at Under 18, Youth, Under 20 and 21 levels, including a junior Grand Slam at Under 20 in 2007, and has now made 55 appearances (55 points) for Leinster. He has nine Irish caps to his credit to date.
SEAN O'BRIEN IN EUROPE: P18 W14 D1 L3
Sean won his second Heineken Cup winners medal in Cardiff last weekend having been an unused replacement in the 2009 final triumph over Leicester Tigers. He made his Heineken Cup debut for Leinster against Castres Olympique on 6 December, 2008, and has now played 18 times in Europe.
Heineken Cup 2008/09
06/12/2008 Rd 3 Leinster 33 - 3 Castres Olympique
17/01/2009 Rd 5 L.Wasps 19 - 12 Leinster
02/05/2009 S-F Munster 6 - 25 Leinster
Heineken Cup 2009/10
09/10/2009 Rd 1 Leinster 9 - 12 London Irish
17/10/2009 Rd 2 Brive 13 - 36 Leinster
12/12/2009 Rd 3 Scarlets 7 - 32 Leinster Try
19/12/2009 Rd 4 Leinster 39 - 7 Scarlets
16/01/2010 Rd 5 Leinster 27 - 10 Brive
23/01/2010 Rd 6 London Irish 11 - 11 Leinster
Heineken Cup 2010/11
09/10/2010 Rd 1 Leinster 38 - 22 Racing Metro (No 6 *) Try
16/10/2010 Rd 2 Saracens 23 - 25 Leinster (No 6)
12/12/2010 Rd 3 Clermont 20 - 13 Leinster (No 6)
18/12/2010 Rd 4 Leinster 24 - 8 Clermont (No 6) Try
15/01/2011 Rd 5 Leinster 43 - 20 Saracens (No 8 *) Try
21/01/2011 Rd 6 Racing Metro 11 - 36 Leinster (No 8 *) Try
09/04/2011 Q-F Leinster 17 - 10 Leicester Tigers (No 7)
30/04/2011 S-F Leinster 32 - 23 Toulouse (No 7)
21/05/2011 Final Leinster 33 - 22 Northampton Saints (No 7)
* = Heineken Man of the match