The Leinster centre, now in pole position to become the British & Irish Lions captain for the tour to South Africa this summer, beat off the challenge from Irish team mates Jamie Heaslip and Paul O'Connell, Italian skipper Sergio Parisse, Welsh full back Lee Byrne and England full back Delon Armitage for the title.
"It has been such an immense week already and to be named the RBS Player of the Championship is a fantastic end to what has been a phenomenal Championship," said O'Driscoll.
"This year's RBS 6 Nations has been a special tournament for me and the team for lots of reasons. It has also been fantastic for Irish rugby and for the whole country.
"To be voted RBS Player of the Championship by the fans makes it extra special, but I'm really proud of our team effort right the way through the tournament and I would not be in this position if it was not for my team mates.
"The support of the fans throughout our campaign has been unwavering and a huge part of the team's success on the pitch. I'm just glad we could reward them too by bringing home the Grand Slam."
The 2009 RBS Player of the Championship was decided as a result of a public vote, hosted on www.rbs6nations.com.
Members of Team RBS (former internationals Jason Leonard, Keith Wood, David Sole, Ieuan Evans, Philippe St Andre and Alessandro Moscardi) each put forward their three recommendations in order of preference and these were combined to create the shortlist.
More than 24,000 fans went online to cast their vote in the online poll - an increase of more than 25% from 2008 - and O'Driscoll garnered nearly 30% of all the votes cast. Like last year, Sergio Parisse (27.9%) was ranked second. O'Driscoll's fellow Irish teammate, Paul O'Connell finished third.
Last year's RBS Player of the Championship was Shane Williams, who went on to amass a hoard of silverware, including the highly coveted IRB Player of the Year award.