Former Bayern Munich forward Lewandowski is only the third player to reach a century of goals in the competition, behind all-time top scorer Cristiano Ronaldo (140) and Lionel Messi (129).
The 36-year-old Poland international was clattered into by Brest goalkeeper Marco Bizot for the spot-kick, which he converted clinically to put Barca 1-0 ahead.
Lewandowski's century of Champions League strikes have come in 125 appearances in the competition, for Borussia Dortmund, Bayern and Barcelona.
Under Hansi Flick the veteran forward's form has improved significantly this season, with the penalty his 21st goal of the campaign in 19 appearances between La Liga and Europe.
Lewandowski has won the Champions League once, with Bayern in 2020, as well as finishing a runner-up with Dortmund in 2013.
© 2024 AFP