Franziska Hartmann was born in Starnberg in 1984 and grew up in Munich. From 2004 to 2008 she studied acting at the Hochschule für Musik und Theater 'Felix Mendelssohn Bartholdy' in Leipzig. Already during this time she occasionally appeared in small television roles as well as in a number of stage productions, for instance at the Chemnitz Theatre. After her graduation she was a member of the ensemble at the Theater Bonn. In 2009 she became a member of the ensemble of the Thalia Theater in Hamburg.   

In addition to her stage work, Hartmann has also been appearing regularly on TV since 2014. After a supporting role in Stefan Krohmer's TV film "Die Zeit mit Euch" (2014) she received a lot of attention for her leading role as a mentally unstable woman in Jan Bonny's "Über Barbarossaplatz" (2016, TV). For her portrayal she was awarded the Actor Prize at the Television Film Festival Baden-Baden together with her co-stars Bibiana Beglau and Joachim Król.   

Following this, she played another central role as the wife of a murderer in the highly acclaimed episode "Borowski und das Fest des Nordens" (2016, directed by Jan Bonny) of the popular "Tatort" series. In Bonny's experimental short film collection "Rheingold" (2016), his short feature film "Es ist egal, aber" (2017) and his terrorism drama "Wintermärchen" ("Germany. A Winter's Tale", 2018) Hartmann also belonged to the ensembles in larger and smaller roles.   

She then played title roles in the episode "Nachtschwester Nina" (2016) of the of the TV series "Helen Dorn", and made guest appearances in episodes of "Der Alte" (2018) and "Tannbach" (2018).    

During the 2018/19 season Franziska Hartmann left the ensemble of the Thalia Theater (where she continues to make guest appearances) and began to work as a freelance actress. In autumn 2019, two films with Franziska Hartmann premiered at Filmfest Hamburg: Stefan Krohmer's "Eine fremde Tochter" (2019, TV), with Hartmann as aunt of the young title character, and Lars Becker's "Wahrheit oder Lüge" (2019, TV), in which she impersonated a presumed rape victim. A little later the social drama "Sterne über uns" ("Stars Above Us", 2019) was released in the cinemas. The film tells the story of a single mother (Hartmann) who tries to lead a "normal" life with her nine- year-old son despite being homeless. Recognized for her outstanding performance in this role, she was awarded the Best Leading Actress Award by the German Television Academy and was nominated for the German Actor Award.

Her notable television roles include an investigative journalist in the "Tatort" episode "Tödliche Flut" (2020), a Hamburg detective in two episodes of the crime series "Helen Dorn" (2021), and a remorseful kindergarten teacher in the drama "Kalt" (2022). Beginning in 2022, Hartmann began her own crime series, "Katharina Tempel," essentially a spin-off featuring the detective character she portrayed in the two "Helen Dorn" crime dramas. Venturing to the other side of the law, Hartmann took on the role of a kidnapper in the "Polizeiruf 110" episode "Du gehörst mir" (2023).

In the drama "Monster im Kopf" ("Monster Inside", 2023), again directed by Christina Ebelt ("Sterne über uns"), Hartmann took on the role of another delinquent: a pregnant prison inmate who is determined to care for her baby against all odds. The film premiered at the Munich Film Festival in June 2023 and was theatrically released in November 2023.