The award will come as some consolation to the 29-year-old flanker following his team's 8-7 defeat to New Zealand in Sunday's World Cup final at Eden Park.
Dusautoir succeeds All Blacks skipper Richie McCaw, who has won the accolade for the past two years, and becomes the first Frenchman to receive the award since Fabien Galthie in 2002.
New world champions New Zealand were not forgotten at Vector Arena, though, taking away the best team title and best coach gong for Graham Henry.
Dusautoir has been outstanding all season for Les Bleus and was superb throughout the World Cup, particularly in the final as his defensive effort and ball-carrying inspired the French against the host nation.
He was picked ahead of five other nominees - New Zealand scrum-half Piri Weepu, flanker Jerome Kaino and centre Ma'a Nonu and Australia flanker David Pocock and scrum-half Will Genia.
The winners were selected by an independent panel of judges, chaired by World Cup winner John Eales and made up of former internationals with more than 500 caps between them.
The panel deliberated on every major Test match played this year, from the first RBS 6 Nations match up to Sunday's Eden Park showpiece.
The glittering awards ceremony, which also celebrated 125 years of the IRB, was a fitting finale to what the organisation's chairman Bernard Lapasset described as an "exceptional" World Cup.
England's George Ford was named IRB junior player of the year, becoming his country's first recipient of the award after playing a key role in his team's run to the Junior World Championship 2011 final in Italy, where they lost 33-22 to New Zealand.
Elsewhere, South Africa's Cecil Afrika picked up the IRB Sevens player of the year accolade, Radike Samo's remarkable individual score for Australia in the final Tri Nations and Bledisloe Cup match against New Zealand was named International Rugby Players' Association try of the year, and former Australia captain George Smith received the IRPA special merit award.
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