In an interview on France 2 television, Lang said he would be "one of the candidates" in the jostling for a Socialist candidate in the presidential race two years from now.
A former culture minister, Lang launched the wildly successful Fete de la Musique, a day-long music spree on June 21 that has been replicated in other European cities.
A slew of polls find Lang among the most popular Socialist figures in France.
One recently suggested he would the toughest opponent of center-right minister Nicolas Sarkozy -- considered France's most popular politician -- if the two were pitted against each other in a presidential race.
If elected president, Lang said he would follow Belgium, Holland, Spain and Canada in pushing through legislation to legalize gay marriages.