The series, which was renewed before the show had even premiered, stars Kelsey Grammer as Chicago's mayor Tom Kane.
Lathan has now signed up for a recurring role in the show, TV Line reports.
Her character Mona is the chief of staff for Alderman Ross (James Vincent Meredith) but soon catches Tom's eye.
Lathan previously starred in Nip/Tuck and has had roles in movies such as Blade and Love & Basketball. She also provides the voice of Donna on The Cleveland Show.
Grammer recently claimed that his Golden Globe win for Boss could help to increase the show's ratings.
The series is due to return to Starz later this year.