Royal, who got 68 percent of the votes, was closely followed by former IMF boss Dominique Strauss-Kahn (64 percent) and Green party presidential candidate Eva Joly (63 percent). The poll was carried out for VSD magazine by Harris Interactive.
Ségolène Royal was the Socialist party's presidential candidate in 2007 when she lost to Nicolas Sarkozy.
She took part in a party contest in October to be the Socialist candidate in next year's presidential election, finishing fourth out of six candidates. The battle was won by her former partner François Hollande.
Strauss-Kahn was once tipped to be the likely Socialist candidate in the upcoming election and polls gave him a clear lead over President Sarkozy.
Those prospects collapsed after he was arrested over the sexual assault of a hotel worker in New York in May. Strauss-Kahn was subsequently cleared of the charges.
Norwegian-born Eva Joly, who was a leading anti-corruption judge in the 1990s, became the Green party's presidential candidate in July.
She is known for her outspoken views, most recently calling far-right Front National leader Marine Le Pen the daughter of a "torturer."
Le Pen's father, Jean-Marie Le Pen, was the founder and leader of the party until January 2011 and previously served in the French Foreign Legion.
President Nicolas Sarkozy finished fourth in the poll, followed closely by Marine Le Pen.