The comic will play the sister of pickup artist Jean Ralphio (Ben Schwartz) in an instalment which sees the character working in Tom Haverford's (Aziz Ansari) Rent-A-Swag store.
Slate is to appear in at least one episode to air in 2013, according to Entertainment Weekly.
She is best known for her role on Bored to Death and a single season of Saturday Night Live.
Parks and Recreation also recently lined up a guest appearance by Moonrise Kingdom actor Jason Schwartzman as the owner of a struggling video store in Pawnee.
US Vice President Joe Biden, US Senator John McCain and Christie Brinkley have also had cameos on the sitcom this season.
NBC airs Parks and Recreation on Thursdays at 8.30/7.30c.