After World War II, she was a member of the ensemble of the Darmstadt State Theatre, between 1948 and 1950 Breidenbach played at the Kiel State Theatre, engagements in Essen, Lucerne, at the Berlin Free Volksbühne, at the Hamburg Ernst Deutsch Theater, at the Schauspielhaus Zürich, at the Stadt- und Ateliertheater in Bern and at the Staatstheater Kassel.
She also appeared in guest roles in series such as Tatort, St. Pauli Landungsbrücken, Auf Achse and Unsere Hagenbecks.
In the animated series Maya the Honey Bee, Tilli Breidenbach was the spokeswoman for the spider Thekla, in the animated series Heidi as Peter's grandmother and in the Muppet Show as the dresser Hilda.
She became known to a wide audience through the role of Lydia Nolte in Hans W. Geißendörfer's family series Lindenstraße.
For health reasons, she was unable to continue her involvement with Lindenstraße, so the role of Lydia Nolte was recast by Ursula Ludwig from episode 410 (first broadcast: 10 October 1993).