The 24-year-old joins Neil Redfearn’s side having come through the ranks at Arsenal Women before moving to Watford Ladies in 2014.
Following two years with Watford Ladies, Leighanne then moved to Millwall in 2016, helping the Lionesses to third place in WSL2 last season.
LFCTV GO: Leighanne Robe discusses new Reds challenge
On moving to Merseyside, Robe said: “I am absolutely delighted to be joining the club and I’m really looking forward to working alongside Neil. It is a massive opportunity to make the step up to WSL1 and I am really excited for the new season.
“Although this is a transition period for the club, Neil has some exciting plans for the future and I have no doubt that we will have a successful season next year. This is a huge club which should be competing for trophies on a regular basis and having spoken to Neil that is definitely the aim of the club.”
Reds manager Redfearn said: “I am delighted to have secured the signature of Leighanne as she is a quality defender who is also a real leader. Leighanne is a tough tackling defender who is equally comfortable playing at full-back so gives us more options in defence.
“I know that a few other clubs in FA WSL1 were looking at signing Leighanne so we are delighted that she has put confidence in our plans for the future and chosen to join Liverpool Ladies.”