He was concertmaster of Orchestra of the Berlin State Opera from 1918 to 1930 and first violinist of the Deman String Quartet which made several recordings.

He formed the Deman String Quartet with Emil Kornsand (second violin), Karl Reitz (viola) and Carl Dechert (cello).

[4][6] In 1930, Deman married the soprano Frida Leider, whom he had met in July 1923 while working together at the Waldoper festival.

[2] To enable his economic survival, Frida Leider tried to support him through guest performances abroad and money sent in a roundabout way.

In 1943, the marriage was officially dissolved, but the couple resumed their marital union in 1946, after Deman's return from exile.

[2] He was buried at the state-owned Heerstraße cemetery near the Olympiapark Berlin in the Bezirk Charlottenburg [de] in what is now the district of Berlin-Westend (grave location: 19-N-26/27).

[2] In 1923 and 1924, he made numerous recordings for Vox, rather light music in duo and trio, but also the Lento from the Violin Concerto by Richard Strauss.