“I simply have the deep belief that my time is up here,” he told the French sports daily.
Galtier, who was appointed in 2017, says he has received job offers from clubs including Nice and Lyon in France and Serie A’s Napoli.
The Marseille-born 54-year-old said he was moving on to avoid “falling into a routine”.
“I feel now is the moment,” he said.
Galtier engineered a turnaround in Lille’s fortunes after succeeding Marcelo Bielsa midway through the 2017-18 season.
Lille just avoided relegation. They then finished second to Paris Saint-Germain in his first full season.
Lille were fourth when last season was ended early because of the coronavirus pandemic, and on Sunday were crowned champions for the first time since 2011.
On the final day of the 2020/2021 season, they beat Angers 2-1 to ensure they finished one point ahead of PSG.
The former Saint-Etienne manager envisages signing up with his next club by the end of the week.
Lille’s fourth Ligue 1 crown ended a three-year league winning streak for PSG, where Mauricio Pochettino took over during the season.
Despite boasting the world’s two most expensive players in Neymar and Kylian Mbappe, PSG had to settle for second best to their more modest rivals from the north of France.
Lille took four points off PSG, beating them in Paris, during the campaign.
Galtier had a year left on his contract, and is moving on with the club facing an uncertain future after turmoil off the pitch during the winter when owner Gerard Lopez was forced to sell due to financial pressure.
Lille also lost Luis Campos, the Portuguese super-scout who built the Monaco team that denied PSG the title in 2017.
Galtier had placed Lille’s success at the door of these two men when he said in November: “The president found funds to invest in players spotted by a man of incredible competence.”
Among the players Campos introduced were Canadian striker Jonathan David and veteran Turkish striker Burak Yilmaz, who both scored in Sunday’s title-clinching win.
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