Weir joined from Manchester City in 2022 but was sidelined for a year after tearing the anterior cruciate ligament in her left knee while playing for Scotland against Belgium in September 2023.
“With your support and that of my team-mates, managers, staff, friends and family, I overcame my knee injury, the biggest setback in my career,” she said on Instagram.
“You also gave me the freedom to become the player and person I am today. For that, I will always be grateful.”
The news of her departure comes two days after she captained Scotland to top spot in their World Cup qualifying group, having scored seven goals in their final two victories over Israel.
Weir, who has netted 31 times in 121 appearances for her country, had won silverware with both City and Arsenal but trophies eluded her in Madrid amid Barcelona dominance, although she was twice voted club player of the season and was a Ballon d’Or Feminin nominee last year.
“The time has come for me to leave this special club,” she said. “I do so with a heart full of love, memories and gratitude.
“My only regret is that I could not give you a first title. I therefore say goodbye with sadness but also excitement to watch from afar and see this club continue to grow.”
