Marianne Sternberg was born in Szeged. Her father, Dezso Sternberg was the founding member of the Sternberg Armin es Testvere factory of music instruments. She was amongst the first female students of the Budapest University of Technology, and graduated in 1924. In 1925, she became the first female member of the Association of Hungarian Engineers and Architects (Magyar Mernok- es Epitesz Egylet, MMEE). Her first important success was an award in the master plan competition of Gyor in 1929. This year she started to use her mother, Ilona's maiden name and sign her works as Marianne Varnay, as a sign of gratitude for her constant support.

In a rare 1929 interview Varnay describes how she tried to get a practicant position in Le Corbusier's Paris office, but was rejected by the master himself for being a woman. Later she worked in the Prague offices of Josef Gocar and Kamil Roskot. She also mentions, that under a friends name she participated and won a competition for worker's housing in Wiener Neustadt, Austria. According to another source, after returning to Budapest she had been a long-time co-worker of well-known architect Jozsef Vago.

In Hungary, her only known works were built in her home city Szeged. In 1935 she won the competition for the local headquarters of the State Social Security Institute (Orszagos Tarsadalombiztositasi Intezet, OTI), and got the commission together with Budapest-based architect Lajos Gyenes. The impressive art deco building on the Tisza Lajos sugarut was finished in 1937. It's facade is decorated with sculptures by another successful female artist of the time, Eva Lote. Around this time Varnay had received a commission to design a new spring house for the Anna forras - unfortunately, this was later demolished. In 1938, she won the competition for the new music center of Szeged.

As part of the modernist movement, she became active in public life, mostly in the topic of women's roles and expectations in the contemporary living environment. In 1932, she held a lecture at the MMEE conference about this topic and in 1937 she published an article in the Magyar Noi Szemle (Hungarian Women's Review) titled 'Modern apartment building and the woman'. She knew and probably collaborated with members of the CIAM and CIRPAC in Hungary, among them Marcel Breuer, and she participated at least one show of the modernists.

She probably died in a concentration camp in 1944, as her name appears among the victims in the USHMM's Holocaust Survivors and Victims Database.