The 20-year-old, who can play as either a full-back or winger, becomes Carla Ward's latest summer addition following on from the arrivals of Christie Murray, Rachel Corsie and Chloe McCarron.
Born in Glasgow, she began her footballing journey as a youth player with Celtic before joining Hibernian in January 2018.
She made a sensational start to her senior career with the Edinburgh club, as she fired home 22 goals in just 33 games and was named as the League's Player of the Year in 2019.
Her displays for Hibs caught the attention of English club Chelsea who snapped her up in December 2019 on a deal which runs until 2021.
Napier made her Chelsea debut in January 2020 after coming off the substitutes' bench during their 3-1 victory against Reading. She made one further appearance for the Londoners ahead of the season being curtailed.
On the international stage she has represented Scotland at Under-17s and Under-19s level and was also called up to the senior squad for the first time last August for a UEFA Women’s Euro 2021 qualifier but has yet to make her senior bow.
Carla Ward’s side line up today against Brighton & Hove Albion (2pm KO) as the new 2020/21 Barclays FA WSL season gets underway.