The soldier alleged Ramon forcibly kissed her after posing at her request for a photograph with her at the prime minister's bureau.
The guilty verdict is expected to lead to a reshuffle of the cabinet of Ehud Olmert, the Israeli prime minister, now his Kadima party colleague would not return.
A Tel Aviv magistrate's court spokeswoman said the three-judge panel decided unanimously to convict Ramon of having carried out an indecent act against the soldier.
The offence occurred on the day Israel went to war with Lebanon last summer.
"We determine that the complainant did not flirt with the accused, did not initiate the kiss and did not consent to it," the court ruling said.
Ramon, who declined to comment to reporters as he left the court building, could face up to three years' imprisonment.
Olmert's office said in a statement: "The prime minister expresses his deep sorrow at the conviction of his friend Haim Ramon."
Israel has been rocked by multiple scandals that have led many Israelis to question whether corruption is rampant within their government.
Women's rights activists have long complained that machoism is pervasive in Israeli society.
Moshe Katsav, the Israeli president, began a leave of absence last week after the attorney-general said he would draft charges against him over allegations he had raped a female employee and sexually assaulted other women who worked for him.
Katsav has denied any wrong-doing in a case that many Israeli feminists see as a significant triumph in a decades-old battle against macho workplace ethics in the Jewish state.
Olmert is being investigated for his role in the 2005 privatisation of an Israeli bank and is also suspected of reportedly appointing cronies to a business authority before he was elected prime minister.
Israel's state comptroller is also examining the terms of his sale of an apartment in Jerusalem.
Olmert has said he did nothing wrong in any of the matters under investigation.
Dan Halutz, Israel's military chief of staff, resigned this month in the wake of a government inquiry into the state leadership's handling of Israel's inconclusive war against Hezbollah guerrillas in Lebanon last summer.
Approval ratings of both Olmert, who is due to testify on Thursday before the Lebanon war commission, and Amir Peretz, the Israeli defence minister and member of the centre-left Labour party, have fallen sharply since the end of the 34-day war.