The 26-year-old joins Palace on a two-year deal ahead of the 2026/27 Barclays Women's Super League season.
The American midfielder played college football for the Stanford Cardinal, before being selected in the second round of the 2023 NWSL Draft by San Diego Wave FC.
She played 18 times for The Wave, helping them to win the NWSL Challenge Cup in 2024.
Enge then moved to Strasbourg in August 2024, ahead of the team's maiden campaign in the French top-flight.
During her two seasons at Le RCS, the former United States Under-23s midfielder made 44 appearances and helped the club to ninth and seventh-place finishes in the French top-flight.
Manager Jo Potter said: "We are delighted to announce Sierra to Palace. She adds real quality and depth to our midfield as we push for success upon our return to the WSL."
Speaking on her move to Palace, Enge said: "The WSL is the best league in the world and to be able to play in it is a dream come true.
"It feels incredible to be at Palace, the facilities are amazing and I'm just really happy to be here."