The 25-year-old defender joins the Reds after three-and-a-half seasons with West Ham United.
She had previously enjoyed a decorated American collegiate career having emerged from the youth system at Millwall Lionesses.
On the international stage Fisk has been capped by England up to U21 level and has previously received call-ups to the senior squad.
She will team up once again with LFC Women manager Matt Beard and managing director Russ Fraser, both of whom she worked with at the Hammers.
“I’m really happy to be here,” the team’s new No.4 told Liverpoolfc.com. “I’ve been walking around the city and just getting used to everything. I’m delighted to be here and can’t wait to get going.
“West Ham was my first professional club and is all I’ve known so far really. I’m 25 now and I wanted to make sure my next contract was the right one for me.
“I know Beardy and Russ previously so when I spoke to them I got a really good feeling. Liverpool as a club, as well, is the type of club you get a feeling from and that’s what I got. So everything sort of fitted to come here.”
Fisk is looking forward to renewing acquaintances with her former boss as the Reds prepare for another season in the Barclays Women’s Super League.
“Beardy, the way he talks and the way he’s so passionate about Liverpool, the players and the whole project, made my decision for me and I think he can really help me develop and push me on to be the best player I can,” she said.
“I love being part of a team, it’s one of the main reasons I play football, I love that feeling of winning together, of training together, and Beardy is really good at bringing everyone together in that. And speaking to the girls, I think Liverpool has that feeling already and I’m looking forward to being a part of it.
“I’m looking forward to fighting for a place and learning from the girls who are here.”
Beard himself is hopeful the move to the Reds will help the centre-back take the next steps in her career.
He said: “Grace is a fantastic defender – reads the game really well, calm and composed, the great thing is she has great vision and great passing range as well.
“Of course, I was lucky to work with her before and it’s been great to see her progress and we’re delighted she’s chosen to come to Liverpool.
“She had a fantastic time in America, going away from home and experiencing something different and then to come back to England and have the career she had at West Ham, hopefully now she can kick on and get back in the England squad as well.”
Fisk is the fifth new signing of the summer window for LFC Women following the arrival of Natasha Flint, Jenna Clark, Mia Enderby and Teagan Micah.