The Fox series starring Nicole Beharie and Tom Mison was renewed earlier this year after a record-breaking premiere on the network, reported Digital Spy.
Jaffrey, best known for her work on 'House of Cards', will join the show as the new sheriff of 'Sleepy Hollow'.
Barr, who has appeared in 'One Tree Hill' and 'Hatfield & McCoys', will play a "ruggedly handsome bounty hunter".
Other actors set to recur on the hit series include Neil Jackson and Victor Garber.
The extended second season of 'Sleepy Hollow' is scheduled to debut this autumn.