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.
Dennis Rodman pledges to end trips to North Korea
Jessica Simpson shares three-way kiss with friends in photo