He was hit in the head and neck, Jerusalem police spokesman Shmuel Ben-Ruby said. Hadassah hospital Professor Shmuel Shapira said Zeevi, 76, was "in very serious condition."
It was not immediately clear who carried out the attack.
Superintendent Ben-Ruby said Zeevi was shot at the Hyatt Hotel as he went to his room on the 8th floor. His wife found him moments later.
The Hyatt hotel is near the border between Jewish and Palestinian neighborhoods in east Jerusalem.
Zeevi, who established the Moledet Party that later formed the Ihud Leumi-Israel Beiteni faction, tendered his resignation Monday.
An opponent of Israeli-Palestinian interim peace agreements, Zeevi protested Prime Minister Ariel Sharon's policies, saying they were too conciliatory. Zeevi advocated a "transfer" of West Bank and Gaza Strip Palestinians.
His resignation was to take effect later Wednesday.