Joining on loan from Chelsea, Gallagher will compete for Palace throughout the 21/22 season.
Speaking with Palace TV having arrived in south London, Gallagher revealed the impact Patrick Vieira had on his decision.
“I spoke to the manager, I liked what he said, I liked how he wants to play, how he wants me to play and how he wants the team to play. I feel like I can learn from him and the players around me. I think that’s the main thing.