Zeevi, a former army general, was shot and killed by members of the Popular Front for the Liberation of Palestine as he was returning to his room at Jerusalem's Hyatt hotel.
The judges ruled that Asmar had "contributed greatly to the assassination", and also found him guilty of being involved in bombing attacks against Israelis.
Last month Hamdi Quran, the gunman who killed Zeevi, was sentenced to 100 years in jail for the assassination, as well as bombing and shooting attacks against Israelis.
Gaza shooting
Separately, Israeli troops shot dead two suspected Palestinians fighters, one of them a woman, near Gaza on Monday, after the two fired at them at a border crossing, army officials said.
The Islamic Jihad said Maissa Fanouna, 23, the first female killed in Gaza since an elderly woman blew herself up near Israeli troops further north over a year ago, was a member.
A third alleged fighter was killed near Jenin in the West Bank, according to Palestinian medical workers.