The 25-year-old is one of the longest serving players in the current Albion squad having joined from Championship side Charlton Athletic in July 2020.
She enjoyed a hugely successful three years at the Addicks prior to the move, helping her side gain promotion to the second tier in 2017/18 before a third-placed Championship finish the season after.
The goalkeeper joins Gareth Taylor’s side in the midst of a fierce title race with only four Barclays Women’s Super League matches left to play.
Manchester City Women Director of Football, Nils Nielsen, said: “We’re really pleased to bring Katie to Manchester City to help us over the coming weeks.
“She has a wealth of experience and a solid track record at a high level, and we believe she is a fantastic player to come in for this period.
“We anticipate that Katie will join us at the City Football Academy next week and we thank her and Brighton & Hove Albion for their help in this situation.”
We would like to welcome Katie to the Club and wish her the very best during her time at City.