In the 1980s, the Romanian authorities allowed him to receive Israeli nationality and he was elected president of the Council of the Jewish Diaspora Museum in Tel Aviv.

He was born on July 23, 1912, in the town of Moineşti, in the district of Bacău, the son of a known rabbi, the rav gaon Avraham Arie Leib Rosen (1870–1951), of Galician origin.

Through the mediation of his son-in-law, the rabbi dr Wolf (Zeev) Gottlieb from Glasgow, his responsa and other religious law works of him were edited and printed in Rav Kook Publishing House in Jerusalem (Shaagat Arié, Eitan Arie, 1912; Pirkei Shoshana, 1920).

But, after September 6, 1940, when the Iron Guard or the Legionnaires, the Romanian extreme right, came to the power, Moses Rosen was arrested under the charge of being "Communist" and deported to an internment camp in Caracal, in the south of Romania.

After several months, after the defeat of the Legionnaires rebellion by the forces loyal to the prime minister, the General Ion Antonescu, Rosen was discharged and fulfilled a part-time job as rabbi in two synagogues in Bucharest – "Reshit Daat" and "Beit El".

After the coup of August 23, 1944, which brought Romania to abandon the alliance with Hitler and put an end to the Fascist-style antisemitic regime, the freedom for Jews was reestablished and Moses Rosen advanced on the steps of the rabbinical hierarchy in Bucharest.

He became the head of the religion department of the Jewish community, was elected as member in the Rabbinate Council and as rabbi of the Great Synagogue of Bucharest (Sinagoga Mare).

In December 1947 the much esteemed Romanian Chief Rabbi in office, Dr Alexandru Şafran, was deported from Romania by the new Communist leadership of the country, which was installed under the pressure of the Soviet occupation force.

Following the item written on the scrap of paper he had pulled out, David Şafran had to give a sample of sermon about the fight for peace on basis of a week pericope from the Torah.

On June 20, 1948, Moses Rosen, as winner of the contest, was installed as "Rav Kolel" in Romania, at a ceremony in the Choral Temple, in the presence of many officials, among them the vice-president of the Great National Assembly (the Romanian parliament under the communist regime), Ştefan Voitec and the minister of religious affairs, Stanciu Stoian.

After his liberation, he was allowed in the end to emigrate to Israel, where he wrote many books, in many of them giving a very negative opinion about Moses Rosen, the "Red rabbi" ("Rabinul roşu").

In 1956, the year when many of the Zionist activists were freed from the Romanian prisons, the authorities allowed Rabbi Rosen to take part again in Jewish meetings and conferences abroad.

Since 1957, Chief Rabbi Rosen, following a renewed tradition existing during the pre-Fascist epoch, was elected member of the Romanian Parliament, representing a Bucharest constituency (then still with a rather large Jewish population).

The Ceauşescu regime decided to strengthen Romania's relations with Israel and with the Jewish communities of the world, especially the United States in order to benefit economically and politically.

With the authorization of the regime and with the help (after 1967) of the Joint Distribution Committee an entire network of institution was founded, such as old-age homes, kosher canteens, medical and social assistance to ill and needy.

[2] Rabbi Rosen, who always felt like a proud Jew, while still being well acquainted with Romanian culture, became one of Romania's non-official "ambassadors" on the international scene.

"[5] In this connection Rabbi Rosen, in his short 1987 piece "The Recipe", quoted Charles de Gaulle: "I have no enemies, I have no friends, I have interests," and added "I succeeded in convincing the Romanian Government that, by doing good to the Jews, by meting out justice to them, it could obtain advantages in matters of favourable public opinion, trade relations, political sympathies...

They did not 'lose their way' heading for other continents..."[6] In the 1980s in his opposition to antisemitism and xenophobic trends which were sometimes encouraged by Ceauşescu himself, Rabbi Rosen dared to raise his voice even against some protégés of the regime, like the poet Corneliu Vadim Tudor, the writer Eugen Barbu and the literary historian Dumitru Vatamaniuc who edited posthumously, and without adequate critic notes, some controversial articles of the Romanian national great poet, Mihai Eminescu which were not favorable towards Jewish people.

[citation needed] After the Romanian Revolution of 1989, Rabbi Rosen was a harsh critic of the efforts to rehabilitate the image of Ion Antonescu, Romania's leader during the period when it had been allied with the Axis Powers during World War II, and continued to advocate emigration to Israel: "Demagogy is very strong here... Neofascist propaganda... plays on xenophobia.

His elder half-brother (from the first marriage of his father) Eliyahu Rosen, was rabbi of the Jews in the Polish town of Oświęcim (Auschwitz) and perished in the Holocaust with his family and whole community.