The 27-year-old joins Albion after three seasons with Rangers, having started her career with Inverness Caledonian Thistle.
She has also had spells with Aberdeen, Hibernian, Yeovil Town, and Glasgow City.
Zoe Johnson, managing director of women’s and girls’ football, said: “We’re delighted to welcome Rachel to the club.
“She’s an experienced player who’s competed in cup finals and the Champions League, as well as on the international stage for Scotland.
“She’s developed her career in the last few seasons with Rangers and we’re looking forward to seeing her thrive in the WSL.”
In her first full season at Rangers, McLauchlan won the SWPL title and was part of the squad that secured a domestic cup double last season, scoring the opening goal in their 2-0 win over Hearts in the Scottish Cup final in May.
She has also been a regular in the Scotland national team in recent years, winning 23 Scotland caps since making her international debut in 2016.