The Warner Bros sequel reunites Robert Downey Jr as Holmes and Jude Law as Dr Watson.
Guy Ritchie is back as director.
The plot is being kept under wraps, although it is known Holmes will face-off against Moriarty.
Also making an appearance will be Holmes' brother, Mycroft.
Rapace's role is shrouded in mystery although sources say the character may be a French Gypsy.
It is unclear if the role is romantic in nature.
Warners is looking to start production later this year.
Holmes 2 is the first acting gig to come to fruition from those meetings.