It was a productive day for the club, with fellow new signing Victor Osimhen, a 20-year-old Nigerian, leading the line and scoring twice as Lille took a 2-1 win over Nantes.
Weah was deployed behind Osimhen from the start and played 68 minutes before being withdrawn in favor of Yusuf Yazici.
The USA international was booked just before being subbed off, but it's a promising start to life at the French club for Weah.
A change of managers during his time in Scotland saw his minutes limited for the Glasgow club as well, leaving him in search of a new home this summer.
Having made his debut for the U.S. national team in March of 2018, Weah's lack of playing time at the club level played a part in him being left out of Gregg Berhalter's roster for the 2019 Gold Cup, which saw the USA lose to Mexico in the final.
Weah did take part in the Under-20 World Cup, scoring the USA's only goal in a 2-1 loss to Ecuador in the quarterfinals.
Earning an opening-day start for Lille, who finished second in Ligue 1 last season and have Champions League football to look forward to this season, is a promising sign for the 19-year-old, who seems very much in the plans for Galtier.
Weah has laid out big goals for himself, saying at his unveiling for the club that he hoped to follow in the footsteps of players like Eden Hazard and Nicolas Pepe, who stared at Lille before going on to become world superstars.
“I’ve known this club since I’ve played in France, and I want to discover its history," he said.
“Great players have come here like Aubameyang, Hazard and (Nicolas) Pepe, and I am very happy to be here. I know that if I work well, I'll improve.
“Now the work begins, and I cannot wait to play in front of the fans. For me, LOSC was the best club – they were second in the championship (last season) and qualified for the Champions League.”