The 19-year-old departed the Tractor Girls this summer, having joining the Blues from Arsenal's academy in 2025.
Seaby was part of the side that won promotion to the Southern Premier Division title and promotion to the second tier for the first time in 2024/25.
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Ruby Seaby, pictured for Ipswich Town Women. (Image: Ross Halls)
She featured for Town in the WSL 2, before spending the second half of 2025/26 on loan at third tier side Lewes.
The young winger now moves up north as she begins the new chapter of her career, linking up Leanne Ross' side, who finished third in the Scottish top-flight last season.
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On signing for her new club, Seaby said: "I'm very excited to get started, buzzing to be here.
"I've heard a lot of good things about the league and I think it's going to push me physically and technically, so I'm excited to test myself."
Glasgow City Head Coach Leanne Ross said: "Ruby is an exciting young player and I'm really excited to bring her exuberance to the squad.
She has pace, is direct with the ball and is also hungry to assist and score goals, bringing the exact qualities that we look for in an attacking player."
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