On 26 August 1939, Kalai ordered the killings of British colonial police officers Ralph Cairns and Ronald Barker via a remotely-detonated Irgun landmine containing fifteen kilograms of blasting gelatin and five kilograms of metal pieces in Rehavia, Jerusalem.

During this period, Kalai also served as a broadcaster on the Irgun's underground radio station, Kol Tsion HaLokhemet.

Menachem Strelitz was a member of the Irgun in Kfar Saba, where he conducted experiments with weapons and explosives.

At the first meeting he chaired, Kalai decided to act on two fronts: to continue retaliatory actions against the Arabs, and the commencement of operations against the British government following Parliament's approval of the White Paper of 1939.

In following this policy, Irgun committed acts of sabotage against the infrastructure, including the post office and the government radio station in Jerusalem.

On August 31, 1939, the British arrested him with other key members of Irgun, including Avraham Stern, during a command meeting in Tel Aviv.

Kalai and Zeroni resigned from Lehi in late 1941 following Stern's attempts to form an alliance with Nazi Germany against the British.

On October 19, 1944, Kalai was exiled to a Kenyan detention camp along with 250 other detainees, and returned to Israel only on July 12, 1948.

He was also an editor and translator to Hebrew from English, German and Yiddish, an editor at the Bialik Institute, a member of the Academy of the Hebrew Language, and the Israel Broadcasting Authority plenum member responsible for Hebrew-language broadcasts.