In the 10th and 11th season of the children's and youth series Die Pfefferkörner (2013/2014) he was seen in a recurring series role as classmate Diego. This was followed by episode roles in the television series Die Kanzlei (2015), Notruf Hafenkante (2017, as a student who blackmails and terrorizes a weaker classmate) and Großstadtrevier (2017, as a former student who takes a Hamburg teacher hostage).
Hilmer also appeared in the film comedy Loneliness and Sex and Pity (2017). The medium-length feature film Final Stage, in which Hilmer played the leading role as teenager Ray, received a Special Jury Prize in the "Perspektive Deutsches Kino" section of the Berlin International Film Festival 2017.
In the Berlin Tatort: Amour Fou (2017) he played a supporting role; he played Stipe Rajic, a Croatian teenager without a high school diploma from a socially deprived district in Berlin-Neukölln, who is unhappily in love with a prospective high school graduate. In the 4th season of the ZDF series Ein Fall für zwei (2017) he was seen as a talented but chaotic student at a high school. In the television series In aller Freundschaft – Die jungen Ärzte (2018), he played an episode lead role as a patient who is admitted to the emergency room with severe abdominal pain. In the 18th season of the ZDF series SOKO Leipzig (2018), Hilmer took on another episode lead role as car apprentice Sammy Kessner, who slips more and more into crime, deals with weapons and rapes the daughter of his instructor.
In 2018, he played the lead role of Cyril in the teen comedy The Most Beautiful Girl in the World, a modern version of the story of Cyrano de Bergerac. Under his role name, he also recorded the song Immer wenn wir uns sehn with the musician Lea and entered the German single charts.
In the TV thriller Der Auftrag (2019), Hilmer played one of the main roles alongside Anja Kling and Gregor Bloéb, the 16-year-old teenager Miki Witt, who witnesses a brutal murder among criminal Berlin clans and is transferred to a witness protection program together with his separated parents. In the three-part ZDF miniseries Preis der Freiheit (2019), Hilmer played the GDR teenager Roland Bohla, who longs for freedom, is imprisoned after a failed escape attempt and finally ransomed and finds his mother in the West. In the ZDFneo disaster series Sløborn (2020), Hilmer was seen in two seasons as the delinquent juvenile Devid. In the war drama Im Westen nichts Neues (2022), Hilmer played one of the main roles as World War II participant Albert Kropp and school friend of the 17-year-old protagonist Paul Bäumer (Felix Kammerer).
Hilmer lives in Hamburg.
