The 18-year-old joined City from Benfica in 2011 and has gradually risen through the ranks at the Etihad Stadium.
Lopes, a Portugal Under-21 international, made four appearances for City last season, making his first start for the club in the 5-0 League Cup win over Wigan Athletic last September.
But the Brazilian-born Lopes will now attempt to gain further first-team experience in northern France after making the temporary switch to the Stade Pierre Mauroy.
Lille will compete in the UEFA Champions League next season, and Lopes is delighted to potentially have the chance to test himself at the top level of European club football.
"I feel very happy to have signed because it is a new step in my career and it is a good opportunity for me to develop as a player," Lopes told City's official website.
"I hope to get much stronger next season, and I'm really looking forward to getting started.
"It is very important for me to play in a professional league for the first time, and it is important for me to experience what it is like to play in that environment.
"It is very different to what I have played in before, but I watched some of the games last year and I think it will be a good league for my development.
"It would be very exciting to be able to play Champions League football. It would be such a good experience for me to play in that competition, a competition which everyone recognises as the best in European football.
"I'm really looking forward to the opportunity."
