A signatory of the Israeli declaration of independence, he worked as editor of Yedioth Ahronoth for more than 35 years.
Born in Kaunas in the Russian Empire (today in Lithuania), Rosenblum moved to Vienna after experiencing antisemitism and being prevented from studying law.
He then moved to London, where he worked as an aide to Ze'ev Jabotinsky, a leader of the Revisionist Zionism movement.
In 1935 he immigrated to Mandate Palestine and started working for the HaBoker newspaper, where he wrote under the pseudonym Herzl Vardi.
After his retirement he published his memoirs, Drops from the Sea (Hebrew: טיפות מן הים, Tipot min HaYam).