Bobb, who worked on the "House of Cards" and "Hostages", will play FBI Agent Gary Burke on the crime drama series, reported Entertainment Weekly.
"He will appear as an FBI agent that Sherlock and Joan audition for. They are looking for work outside the department. Jeremy plays someone that Joan got to know when Sherlock left to work with MI6 last year," executive producer Rob Doherty said.
The actor will appear in the second episode of season four, though there is potential for him to return.
"He's fantastic. I'd like to think that if we do more work with the FBI this year, we could do more work with Jeremy," Doherty said.