Marcelo Bielsa's side are two points clear of Lyon in second, and three above champions PSG in third, at the mid-season break.
After edging Lille 2-1 on Sunday, Gignac said it was an achievement to savour to see last season's sixth-placed side in charge of the league.
"To be honest, it's so good... a wonderful feeling. It is so amazing because it has been ages since Marseille have been the winter champions," Gignac said.
"And even if it is not a title, and it is just a symbol, but it is a huge boost for our confidence.
"It is a great joy for our supporters to be in front of Paris at halfway of the season.
"It is the best gift we could offer them before the break."
Defender Benjamin Mendy, who has played 90 minutes in all bar one of Marseille's league matches this term, said their standing at the top was no fluke.
"We deserve to be where we are," Mendy said.
"Some people doubt us as we lost against big teams like Monaco, Lyon or PSG.
"What matters to us is today we are still first in the league. That was our main concern.
"We lost important points against those big teams but we found the strength to bounce back and win games regularly."
Michy Batshuayi, who scored what proved to be the winner in the 69th minute on Sunday, said he savoured the atmosphere in his first Ligue 1 start.
"I had a great time playing that position [playmaker] and being on the pitch in that ambiance," Batshuayi said.
"I am so happy because I am more used to watching them rather than being at the heart of the game. I am thrilled and I hope we will carry on like that."
