Quirk arrives at the club having won the Championship’s Rising Star award after the 2024/25 season, after scoring five goals in 20 games for Pompey.
She also played an important role as Portsmouth won the FA Women’s National League Southern Premier Division in 2023/24 – the league the Cherries will play in this season.
In that season, Quirk netted 19 goals and notched 18 assists in 29 appearances in Hampshire.
Previously, the 23-year-old has played for Charlton Athletic in the second tier, as well as London Bees and Reading.
Quirk told afcb.co.uk: “I am really excited and buzzing to be here. The club did really well last season and, on first impressions, everyone has been really nice.
_(Image: AFC Bournemouth)_ “With the club winning the league at tier four, when you’ve won anything, it gives you the mentality to keep going.
“The club is pushing in the right direction and everyone wants to win, there’s no two ways about it and we are really excited to finish as high as we can next season.
“Seeing how the club has gone two league seasons unbeaten. That shows the mentality of the club in that they are really invested in the women’s team. It’s positive and exciting.
“The style of play in the team also drew me into joining. When I played at Portsmouth, we got beaten two times by AFC Bournemouth.
“You know what the club is about and know there is a lot of fight and spirit about the club. You know they are a winning club.”
Manager Steve Cuss said: “We are really pleased to bring in someone of Sophie’s quality and pedigree to join our squad at AFC Bournemouth.
“Her record in terms of goals and assists speaks for itself, as well as the fact she was an award winner in the second tier last season.
“She is a proven winner in the division we will be competing in this season, making her a really important addition to the group.”