O'Driscoll, who started the first and second Tests for the 2009 Lions before injury ended his tour a week early, was an overwhelming winner of the prestigious award.
The 31-year-old centre polled 90 percent of the votes to reaffirm his position as one of the leading lights in world rugby.
O'Driscoll becomes only the third Irish winner of the trophy and the first for nearly a quarter of a century, following in the footsteps of fellow Lions Ollie Campbell (1982) and the late Mick Doyle (1985).
The past 12 months have seen O'Driscoll win the Heineken Cup with Leinster and lead Ireland to a first Grand Slam in 61 years, before again starring for the Lions on the big stage.
He was considered unfortunate by many to miss out on the IRB World Player of the Year award to All Black openside Richie McCaw but few would bet against him making a fourth consecutive Lions tour if he is still playing in 2013.
Although he wasn't able to travel to the Tower Hotel in London to receive his award in person, O'Driscoll sent a video message to the 500-strong gathering which included a tribute to Lions coach Sir Ian McGeechan, who received a Special Award for his services to the game from the Rugby Union Writers' Club.
First formed in 1960, the RUWC instituted the Pat Marshall Memorial Award in the 1975/76 season in memory of the great Daily Express rugby writer. The first winner was Wales and Lions No 8 Mervyn Davies.
Pat Marshall Memorial Award winners
1975/76 Mervyn Davies (Swansea / Wales)
1976/77 Andy Irvine (Heriot's FP / Scotland)
1977/78 Gareth Edwards (Cardiff / Wales)
1978/79 JPR Williams (Bridgend / Wales)
1979/80 Bill Beaumont (Fylde / England)
1980/81 Jean-Pierre Rives (Toulouse / France)
1981/82 Ollie Campbell (Old Belvedere / Ireland)
1982/83 Dave Loveridge (Taranaki / New Zealand)
1983/84 Jim Aitken (Gala / Scotland)
1984/85 Mick Doyle (Ireland coach)
1985/86 Jonathan Davies (Neath / Wales)
1986/87 David Kirk (Auckland / New Zealand)
1987/88 Rob Norster (Cardiff / Wales)
1988/89 Finlay Calder (Stewart's-Melville FP / Scotland)
1989/90 Ian McGeechan (Scotland coach)
1990/91 David Campese (NSW / Australia)
1991/92 Nick Farr-Jones (NSW / Australia)
1992/93 Ben Clarke (Bath / England)
1993/94 Francois Pienaar (Transvaal / South Africa)
1994/95 Jonah Lomu (Counties / New Zealand)
1995/96 Sean Fitzpatrick (Auckland / New Zealand)
1996/97 Lawrence Dallaglio (London Wasps / England)
1997/98 Nick Mallett (South Africa coach)
1998/99 Tim Horan (Queensland / Australia)
1999/00 Pat Lam (Northampton Saints / Samoa)
2000/01 Martin Johnson (Leicester Tigers / England)
2001/02 Martin Johnson (Leicester Tigers / England)
2002/03 Jonny Wilkinson (Newcastle Falcons / England)
2003/04 Martin Johnson (Leicester Tigers / England)
2004/05 Rob Howley (London Wasps / Wales)
2005/06 Gareth Thomas (Toulouse / Wales)
2006/07 Jason White (Sale Sharks / Scotland)
2007/08 Jason Robinson (Sale Sharks / England)
2008/09 Shane Williams (Ospreys / Wales)
2009/10 Brian O'Driscoll (Leinster / Ireland)