The English actress - most recently seen as Roya Hammad on Homeland - will play brilliant scientist Dr Sonia Kidd, TVLine reports.
When one of her students is murdered, Kidd crosses paths with Patrick Jane (Simon Baker) and the CBI team.
Robinson previously appeared on HBO's Rome and X-Files spinoff The Lone Gunmen, while her film credits include 2000's Timecode and 2004's Hidalgo opposite Viggo Mortensen.
The 35-year-old joins Supernatural actor Rob Benedict and 24's Mary Lynn Rajskub in signing up for a role on the fifth season of The Mentalist.
The series returns to CBS this Sunday (January 6), while new episodes air in the UK on Channel 5.
> 'The Mentalist' Owain Yeoman Q&A: 'We'll come within inches of Red John'
Watch a promo for the return of The Mentalist below: