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.
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.